JP7750761B2 - Electrically heated carrier and exhaust gas purification device - Google Patents

Description

The present invention relates to an electrically heated carrier. The present invention also relates to an exhaust gas purification device that uses an electrically heated carrier.

In recent years, electrically heated catalysts (EHCs) with honeycomb structures have been proposed to alleviate the decline in exhaust gas purification performance immediately after engine start-up. EHCs generally comprise an outer peripheral wall, a conductive honeycomb structure portion disposed inside the outer peripheral wall and having partition walls that define multiple cells that form flow paths from one end face to the other, and a pair of electrode layers disposed on the outer peripheral wall of the honeycomb structure portion. In EHCs, it is desirable to control the temperature distribution within the honeycomb structure portion, and various technologies have been developed.

Patent Document 1 (JP 2014-198321 A) describes that a honeycomb structure is composed of a peripheral region including the side surfaces and a central region excluding the peripheral region, and that the electrical resistivity of the material constituting the peripheral region is lower than the electrical resistivity of the material constituting the central region. By making the electrical resistivity of the peripheral region lower than that of the central region, it is believed that when a voltage is applied to the honeycomb structure, current from the electrodes flows more easily to the honeycomb structure (carrier), making it easier for the honeycomb structure to generate heat uniformly.

Patent Document 2 (JP 2014-198446 A) describes that the honeycomb structure is composed of a peripheral region including the side surfaces and a central region that is the center region excluding the peripheral region, and that the electrical resistivity of the central region is lower than that of the peripheral region. With this configuration, the electrical resistivity of the central region is lower than that of the peripheral region, so that when a voltage is applied to the honeycomb structure, more current flows in the inlet region, and the current that flows due to the applied voltage can be used effectively to treat substances in the exhaust gas.

Patent Document 3 (JP 2019-173663 A) describes that the honeycomb structure is composed of a peripheral region including the side surfaces, a central region, and an intermediate region excluding the peripheral and central regions, and that the average electrical resistivity A of the material comprising the peripheral region, the average electrical resistivity B of the material comprising the central region, and the average electrical resistivity C of the material comprising the intermediate region satisfy the relationship A≦B<C. This configuration is said to improve the uniform heat generation of the honeycomb structure.

Patent Document 4 (JP 2019-173662 A) describes that the honeycomb structure is composed of end regions near a pair of electrode sections and a central region excluding the end regions, and that the average electrical resistivity A of the material that composes the end regions is lower than the average electrical resistivity B of the material that composes the central region. This configuration is said to improve the uniform heat generation of the honeycomb structure.

JP 2014-198321 A JP 2014-198446 A Japanese Patent Application Laid-Open No. 2019-173663 Japanese Patent Application Laid-Open No. 2019-173662

As such, various technologies have been proposed for controlling the temperature distribution in a honeycomb structure. However, there is still room for improvement in terms of heat generation uniformity within the honeycomb structure. In the technology described in Patent Document 1, the electrical resistivity of the peripheral region is lower than that of the central region, which makes it easier for current to flow in the peripheral region and increases the temperature in the peripheral region. The technology described in Patent Document 2 does not aim for heat generation uniformity, and the temperature near the electrodes increases. In the technology described in Patent Document 3, the average electrical resistivity A of the material constituting the peripheral region is low, which also makes it easier for current to flow in the peripheral region and still increases the temperature in the peripheral region. In the technology described in Patent Document 4, current concentrates in the edge regions near the pair of electrodes and does not spread to the left or right, which makes it easier for the temperature to decrease in the peripheral region away from the region sandwiched between the pair of electrodes in a cross section perpendicular to the extension direction of the cell.

The present invention was created in light of the above circumstances, and in one embodiment, it is an object of the present invention to provide an electrically heated carrier with improved heat generation uniformity. In another embodiment, it is an object of the present invention to provide an exhaust gas purification device equipped with such an electrically heated carrier.

The above problems can be solved by the present invention, which will be exemplified below.
[1]
a conductive honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells that form flow paths from one end face to the other end face;
a first electrode layer provided in a strip shape on the surface of the outer peripheral wall in the extending direction of the cell; and
a second electrode layer provided in a strip shape on the surface of the outer peripheral wall in the extending direction of the cells, the second electrode layer being provided so as to face the first electrode layer across the central axis of the honeycomb structure section;
Equipped with
In a cross section perpendicular to the cell extension direction, the honeycomb structure portion has
a first resistive region having a contact to the first electrode layer;
a second resistive region having a contact to the second electrode layer; and
a third resistance region that does not contact either the first electrode layer or the second electrode layer and crosses the cross section so as to be sandwiched between the first resistance region and the second resistance region;
the third resistance region has a higher electrical resistance per unit volume (1 cm ³ ) than ^the first resistance region and the second resistance region;
Electrically heated carrier.
[2]
[1] An electrically heated carrier according to the present invention;
and a cylindrical metal tube that houses the electrically heated carrier.

One embodiment of the present invention provides an electrically heated carrier with improved heat generation uniformity. As a result, it is possible to reduce temperature differences in the honeycomb structure, which also helps prevent cracks from occurring. This electrically heated carrier can be used, for example, as a catalyst carrier in an exhaust gas purification device.

1 is a schematic diagram of an electrically heated carrier according to one embodiment of the present invention, observed from one end face. 1 is a schematic perspective view of an electrically heated carrier according to an embodiment of the present invention; 1 is a schematic diagram for explaining a method for identifying each resistance region in a cross section perpendicular to the extension direction of the cells of an electrically heated carrier according to one embodiment of the present invention. FIG. 3 is a schematic diagram showing an example of the arrangement of each resistance region in a cross section perpendicular to the extension direction of the cells of the electrically heated carrier according to one embodiment of the present invention. FIG. 10 is a schematic diagram showing an example of the arrangement of each resistance region in a cross section perpendicular to the extension direction of the cells of an electrically heated carrier according to another embodiment of the present invention. FIG. FIG. 10 is a schematic diagram showing an example of the arrangement of each resistance region in a cross section perpendicular to the extending direction of the cells of an electrically heated carrier according to yet another embodiment of the present invention. FIG. 10 is a schematic diagram showing an example of the arrangement of a plurality of slits in a cross section perpendicular to the extending direction of the cells of an electrically heated carrier according to yet another embodiment of the present invention.

Next, embodiments of 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 and improvements may be made based on the common knowledge of those skilled in the art without departing from the spirit of the present invention.

(1. Electrically heated carrier)
Fig. 1A is a schematic diagram of an electrically heated carrier 100 according to one embodiment of the present invention when viewed from one end surface 116. Fig. 1B is a schematic perspective view of the electrically heated carrier 100 according to one embodiment of the present invention.
The electrically heated carrier 100 is
a conductive honeycomb structure portion (110) having an outer peripheral wall (114) and partition walls (113) disposed inside the outer peripheral wall (114) and defining a plurality of cells (115) that form flow paths from one end face (116) to the other end face (118);
a first electrode layer 112a provided in a strip shape on the surface of the outer peripheral wall 114 in the extension direction of the cells 115; and a second electrode layer 112b provided in a strip shape on the surface of the outer peripheral wall 114 in the extension direction of the cells 115, the second electrode layer 112b being provided so as to face the first electrode layer 112a across the central axis O of the honeycomb structure section 110.
Equipped with.

The electrically heated carrier 100 may be used as a catalyst body by supporting a catalyst on the electrically heated carrier 100. A fluid such as automobile exhaust gas can flow through the multiple cells 115. Examples of the catalyst include precious metal catalysts and other catalysts. Examples of precious metal catalysts include three-way catalysts and oxidation catalysts in which precious metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are supported on the pore surfaces of alumina and contain promoters such as ceria and zirconia, and _NOx storage reduction catalysts (LNT catalysts) containing alkaline earth metals and platinum as nitrogen oxide ( _NOx ) storage components. 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 catalysts on honeycomb structures.

(1-1. Honeycomb structure part)
The honeycomb structure 110 has an outer peripheral wall 114 and partition walls 113 disposed inside the outer peripheral wall 114 to define a plurality of cells 115 that form flow paths from one end face 116 to the other end face 118. The honeycomb structure 110 is a conductive columnar member. A columnar shape can be understood as a three-dimensional shape having a thickness in the direction in which the cells extend (the axial direction of the honeycomb structure). The ratio (aspect ratio) of the axial length of the honeycomb structure to the diameter or width of the end face of the honeycomb structure is arbitrary. The columnar shape may also include a shape (flat shape) in which the axial length of the honeycomb structure is shorter than the diameter or width of the end face.

The outer shape of the honeycomb structure part 110 can be, for example, 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. Furthermore, the size of the honeycomb structure part 110 is preferably such that the area of one end face is 2000 to 20000 ^mm2 , more preferably 5000 to 15000 ^mm2 , for the reason of increasing heat resistance (suppressing cracks that extend in the circumferential direction of the outer peripheral wall).

There are no particular restrictions on the height of the honeycomb structure portion 110 (the length from one end face 116 to the other end face 118), and it can be set appropriately depending on the application and required performance.

Providing an outer peripheral wall 114 on the honeycomb structure 110 is useful in ensuring the structural strength of the honeycomb structure 110 and in preventing leakage of fluid flowing through the cells 115 from the outer peripheral wall 114. In this regard, the thickness of the outer peripheral wall 114 is preferably 0.1 mm or more, more preferably 0.15 mm or more, and even more preferably 0.2 mm or more. However, if the outer peripheral wall 114 is made too thick, it will have too much strength, which will disrupt the strength balance with the partition walls 113 and reduce thermal shock resistance. Therefore, the thickness of the outer peripheral wall 114 is preferably 1.0 mm or less, more preferably 0.7 mm or less, and even more preferably 0.5 mm or less. Here, the thickness of the outer peripheral wall 114 is defined as the thickness in the direction normal to the tangent to the outer surface of the outer peripheral wall 114 at the measurement point when the portion of the outer peripheral wall 114 where the thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cells 115.

The outer peripheral wall 114 and the partition walls 113 have a higher volume resistivity than the electrode layers 112a and 112b, but are conductive. There are no particular restrictions on the volume resistivity of the outer peripheral wall 114 and the partition walls 113, as long as they can generate heat by Joule heat when current is applied, but a volume resistivity of 0.1 to 200 Ωcm is preferred, a volume resistivity of 1 to 200 Ωcm is more preferred, and a volume resistivity of 10 to 100 Ωcm is even more preferred.

2, the honeycomb structure part 110 can be classified into the following three regions in a cross section perpendicular to the extension direction of the cells 115. It is preferable that the honeycomb structure part 110 be classified into the following three regions in any cross section perpendicular to the extension direction of the cells 115.
A first resistor region 110A having a contact to the first electrode layer 112a
A second resistor region 110B having a contact to the second electrode layer 112b
a third resistance region 110C that does not contact either the first electrode layer 112a or the second electrode layer 112b, and that traverses the cross section so as to be sandwiched between the first resistance region 110A and the second resistance region 110B, and that has a higher electrical resistance per unit volume (1 cm ³ ) than the electrical resistance per unit volume (1 cm ³ ) of the first resistance region 110A and the second resistance region 110B;

Although the present invention is not intended to be limited by theory, a possible mechanism for improving heat generation uniformity in the honeycomb structure 110 according to this embodiment will be considered. First, when the electrical resistance in the honeycomb structure 110 is constant regardless of location, the temperature near the first electrode layer 112a and the second electrode layer 112b, which are the current inlets and outlets, tends to be high, while the temperature near the center of the honeycomb structure tends to be low. In addition, the temperature in the peripheral area away from the area sandwiched between the first electrode layer 112a and the second electrode layer 112b also tends to be low.
In contrast, in the case of a honeycomb structure section 110 having a first resistance region 110A, a second resistance region 110B, and a third resistance region 110C, the third resistance region, which has a relatively high electrical resistance, does not have a portion in contact with either the first electrode layer 112a or the second electrode layer 112b. In other words, the first resistance region 110A and the second resistance region 110B, which have low electrical resistance, are in contact with the first electrode layer 112a and the second electrode layer 112b, respectively, thereby suppressing excessive heat generation near the first electrode layer 112a and the second electrode layer 112b. On the other hand, the third resistance region 110C, which includes the central axis O of the honeycomb structure section 110, has a high electrical resistance, and therefore generates a larger amount of heat for the same amount of current. This improves heat generation uniformity.
Furthermore, since the third resistance region 110C traverses the cross section of the honeycomb structure section 110, when a voltage is applied between the first electrode layer 112a as the anode and the second electrode layer 112b as the cathode, the current flowing from the first electrode layer 112a to the second electrode layer 112b always passes through the third resistance region 110C, which has a high electrical resistance. In other words, in the honeycomb structure section 110 according to this embodiment, there is no escape route for the current in the outer periphery, so the current can flow with high uniformity in both the outer periphery and the center.
Therefore, according to the honeycomb structure section 110 of this embodiment, the heat generation uniformity is improved when a voltage is applied between the first electrode layer 112a and the second electrode layer 112b.
The same can be said for applying a voltage between the first electrode layer 112a as the cathode and the second electrode layer 112b as the anode.

The electrical resistance per unit volume (1 cm ³ ) of each resistance region is measured at room temperature (25° C.) according to the four-terminal method.

In a cross section perpendicular to the extension direction of the cell 115, the first resistance region 110A, the second resistance region 110B, and the third resistance region 110C can be identified as follows: First, a line segment M is drawn from the central axis O of the cross section toward the circumferential center of either the first electrode layer 112a or the second electrode layer 112b. Next, a square S having an area of 1 ^cm2 and a pair of sides parallel to the line segment M is drawn, with the central axis O as its center of gravity. Next, eight squares each having an area of 1 ^cm2 are drawn, each sharing one side with square S and adjacent to square S. Next, another square each having an area of 1 ^cm2 is drawn, each sharing one side with each of these eight squares. This process is repeated to divide the cross section into ¹ cm2 squares. Figure 2 shows a schematic diagram of the honeycomb structure section 110 divided into a large number of adjacent 1 ^cm2 squares.

A rectangular parallelepiped sample with a depth of 3 cm and a size of ^{3 cm} is taken from each 1 ^cm2 square that divides the cross section, and the electrical resistance of the rectangular parallelepiped sample is measured using the method described above, and then the electrical resistance per 1 ^cm3 is calculated. There may be areas on the periphery where it is not possible to take a 3 ^cm3 rectangular parallelepiped, but samples are taken from such areas to the extent that they can be taken, and the electrical resistance of the sample is measured using the method described above and converted to electrical resistance per 1 ^cm3 based on the volume ratio. Note that if the electrical resistance of the sample is known or clear, there is no need to take a sample.

By the above procedure, the electrical resistance per 1 ^cm3 of each of the 1 ^cm2 square sections when the cross section of the honeycomb structure section 110 is divided is obtained. Next, the electrode layer having an intersection with the line segment M is defined as the first electrode layer 112a, and a square section T including the surface point of the outer wall 114 that contacts the circumferential center of the first electrode layer 112a is identified. If the electrical resistance per 1 ^cm3 of the square section T (excluding the electrode layer) is defined as R _T , the set of square sections of the honeycomb structure section that are continuous with the square section T and have an electrical resistance in the range of R _T × 0.6 or more and less than R _T × 1.1 is defined as the first resistance region 110A.

Furthermore, in the above cross section, a square U encompassing the surface point of the outer peripheral wall 114 that contacts the circumferential center of the second electrode layer 112b facing the first electrode layer 112a is identified, and the set of compartments of the honeycomb structure part that are continuous with the compartment of the square U and have an electrical resistance in the range of _R × 0.6 or more and less than _R × 1.1 is defined as the second resistance region 110B. Note that the standard of electrical resistance used to identify the second resistance region 110B is R, not _R , which is the electrical resistance per ^cm3 of the compartment of the square U (excluding the electrode _layer ).

Furthermore, in the above cross section, if a region is identified that crosses the cross section so as to be sandwiched between the first resistance region 110A and the second resistance region 110B without contacting either the first electrode layer 112a or the second electrode layer 112b, and if the electrical resistance of each section of the honeycomb structure part included in this region is always R _T × 1.1 or more, then this region can be recognized as a third resistance region.

Methods for relatively increasing the electrical resistance per unit volume (1 ^cm3 ) in the third resistance region 110C include, but are not limited to, a method of making the thickness of the partition walls 113 in the third resistance region 110C thinner than the thicknesses of the partition walls in the first resistance region 110A and the second resistance region 110B. Such a partition wall structure in the second resistance region 110B can be realized by designing the die structure used when extruding the honeycomb structure section so that the desired partition wall thickness is obtained in each resistance region. Another possible method is to provide slits formed by removing some of the partition walls 113 in the third resistance region 110C. In this case, too, this can be realized by designing the die structure used when extruding the honeycomb structure section so that removed slits are formed in some of the partition walls in the third resistance region 110C.

It is desirable that the electrical resistance per unit volume (1 ^cm3 ) of the multiple compartments of the honeycomb structure portion constituting the first resistance region 110A and the second resistance region 110B fluctuate little. This is because, for the first resistance region 110A and the second resistance region 110B, large fluctuations in electrical resistance within the same resistance region will cause the current flow to become uneven, reducing the effect of improving heat generation uniformity. Specifically, in the above cross section, the ratio of the maximum electrical resistance _Rmax to the minimum electrical resistance Rmin per unit volume (1 ^cm3 ) of the multiple square compartments constituting each resistance region of the first resistance region _110A and the second resistance region 110B preferably satisfies 1.0≦ _Rmax / _Rmin ≦2, more preferably 1.0≦ _Rmax / _Rmin ≦1.6, and even more preferably 1.0≦ _Rmax / _Rmin ≦1.3.

For the third resistance region 110C as well, large variations in electrical resistance within the region can lead to a reduction in the effect of improving heat generation uniformity. Therefore, in the above cross section, the ratio of the maximum electrical resistance _Rmax to the minimum electrical resistance _Rmin per unit volume (1 ^cm3 ) of the multiple square compartments constituting the third resistance region 110C preferably satisfies 1.0≦ _Rmax / _Rmin ≦2, more preferably 1.0≦ _Rmax /Rmin≦ _1.6 , and even more preferably 1.0≦ _Rmax / _Rmin ≦1.3.

FIG. 3 is a schematic diagram showing an example of the arrangement of each resistance region (110A, 110B, 110C) in a cross section perpendicular to the cell extension direction of an electrically heated carrier according to one embodiment of the present invention. In the embodiment shown in FIG. 3, when the cross section perpendicular to the cell extension direction is observed with the first electrode layer 112a located on the upper side and the second electrode layer 112b located on the lower side, the third resistance region 110C crosses the cross section perpendicular to the cell extension direction from left to right so as to be sandwiched between the first resistance region 110A and the second resistance region 110B. The third resistance region 110C is formed in a strip shape with a constant width in the vertical direction. In this case, if the electrical resistance per unit volume (1 cm ³ ) of the multiple square compartments forming the third resistance region 110C is constant, the amount of current and the amount of heat generated are likely to be smaller in the outer periphery of the honeycomb structure section 110 than in the vicinity of the central axis O.

Therefore, it is preferable to increase the amount of current in the outer periphery of the third resistance region 110C to increase the amount of heat generated in the outer periphery and further improve the heat generation uniformity. One method for increasing the amount of current in the outer periphery of the third resistance region 110C is to lower the electrical resistance per unit volume (1 ^cm3 ) in the region of the third resistance region 110C that corresponds to the outer periphery of the honeycomb structure section 110. Figure 4 is a schematic diagram showing an example of the arrangement of each resistance region (110A, 110B, 110C) in a cross section perpendicular to the extension direction of the cells of an electrically heated carrier according to another embodiment of the present invention.

In the embodiment shown in FIG. 4, when a cross section perpendicular to the cell extension direction is observed with the first electrode layer 112a positioned on the upper side and the second electrode layer 112b positioned on the lower side, the third resistance region 110C is
a central portion 110C1 including the central axis O of the honeycomb structure portion 110;
a left side portion 110C2 adjacent to the left end of the central portion 110C1, extending to the left end of the third resistance region 110C, and having a lower electrical resistance per unit volume (1 cm ³ ) than the central portion 110C1; and a right side portion 110C3 adjacent to the right end of the central portion 110C1, extending to the right end of the third resistance region 110C, and having a lower electrical resistance per unit volume (1 cm ³ ) than the central portion 110C1.
It is classified into three areas:

The distinction between the central portion 110C1 and the left portion 110C2, and the distinction between the central portion 110C1 and the right portion 110C3 can be determined as follows. First, the third resistance region 110C is determined using the procedure described above. Next, the electrical resistance per ^cm3 corresponding to the square S described above is used as a reference resistance, and within the third resistance region 110C, the aforementioned sections having an electrical resistance of 90% or less of the reference resistance are determined as low-resistance regions. The remaining sections forming the third resistance region 110C are determined as high-resistance regions. Then, when the low-resistance regions and high-resistance regions are arranged from left to right in the order of low-resistance region → high-resistance region → low-resistance region as shown in FIG. 4, the low-resistance region on the left can be determined as the left portion 110C2, the high-resistance region in the center can be determined as the central portion 110C1, and the low-resistance region on the right can be determined as the right portion 110C3.

The ratio of the average value of electrical resistance per unit volume (1 cm ³ ) in the central portion 110C1 to the average value of electrical resistance per unit volume (1 cm ³ ) in the left portion 110C2 is preferably 1.15-4, more preferably 1.15-2.
The ratio of the average value of electrical resistance per unit volume (1 cm ³ ) in the center portion 110C1 to the average value of electrical resistance per unit volume (1 cm ³ ) in the right portion 110C3 is preferably 1.15-4, more preferably 1.15-2.
The ratio of the average electrical resistance per unit volume (1 cm ³ ) in the right portion 110C3 to the average electrical resistance per unit volume (1 cm ³ ) in the left portion 110C2 is preferably 0.8 to 1.2, and more preferably 0.9 to 1.1. It is particularly preferable that the average electrical resistance per unit volume of the left portion 110C2 and the right portion 110C3 be approximately the same.

Another method for increasing the amount of current in the peripheral portion of the third resistance region 110C is to narrow the vertical width of the region of the third resistance region 110C that corresponds to the peripheral portion of the honeycomb structure portion 110. Figure 5 is a schematic diagram showing an example of the arrangement of each resistance region (110A, 110B, 110C) in a cross section perpendicular to the extension direction of the cells of an electrically heated carrier according to yet another embodiment of the present invention.

In the embodiment shown in FIG. 5, when a cross section perpendicular to the cell extension direction is observed with the first electrode layer 112a positioned on the upper side and the second electrode layer 112b positioned on the lower side, the third resistance region 110C is
a central portion 110C1 including the central axis O of the honeycomb structure portion 110;
a left side portion 110C2 adjacent to the left end of the central portion 110C1, extending to the left end of the third resistance region 110C, and having a narrower width in the vertical direction than the central portion 110C1; and a right side portion 110C3 adjacent to the right end of the central portion 110C1, extending to the right end of the third resistance region 110C, and having a narrower width in the vertical direction than the central portion 110C1.
It is classified into three areas:

In both the embodiments shown in Figures 4 and 5, the horizontal length of the center portion 110C1 of the third resistance region 110C may be set appropriately, taking into account the distribution of heat generation. However, in the third resistance region 110C, current tends to flow toward the inside of the horizontal width of the first electrode layer 112a and the second electrode layer 112b, resulting in a smaller amount of heat generation outside of that width. For this reason, it is preferable to promote an increase in the amount of current outside the horizontal width of the first electrode layer 112a and the second electrode layer 112b. Therefore, in a preferred embodiment, the right end of the center portion 110C1 of the third resistance region 110C is located to the right of the right edge of the first electrode layer 112a in the circumferential direction and to the right of the right edge of the second electrode layer 112b in the circumferential direction. Furthermore, the left end of the center portion 110C1 of the third resistance region 110C is located to the left of the left edge of the first electrode layer 112a in the circumferential direction and to the left of the left edge of the second electrode layer 112b in the circumferential direction.

4 , in a cross section perpendicular to the cell extension direction, a line N is drawn that passes through the central axis O and is perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. On line N, the length of the third resistance region 110C located to the right of the right circumferential end of the first electrode layer 112a (second electrode layer 112b) is defined as a, and the length of the third resistance region 110C that is occupied by the central portion 110C1 of the third resistance region 110C is defined as b. In this case, the ratio b/a can be, for example, 0.05≦b/a≦0.95, and typically 0.1≦b/a≦0.9.
Similarly, the length of the third resistance region 110C located on the left side of the outer circumferential left end of the first electrode layer 112a (second electrode layer 112b) on the line N is defined as c, and the length of the central portion 110C1 of the third resistance region 110C is defined as d. In this case, for example, 0.05≦d/c≦0.95 can be satisfied, and typically 0.1≦d/c≦0.9 can be satisfied.

5 , in a cross section perpendicular to the cell extension direction, a line N is drawn that passes through the central axis O and is perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. On line N, the length of the third resistance region 110C located to the right of the right circumferential end of the first electrode layer 112a (second electrode layer 112b) is defined as a, and the length of the third resistance region 110C that is occupied by the central portion 110C1 of the third resistance region 110C is defined as b. In this case, the ratio b/a can be, for example, 0.05≦b/a≦0.95, and typically 0.1≦b/a≦0.9.
Similarly, the length of the third resistance region 110C located on the left side of the outer circumferential left end of the first electrode layer 112a (second electrode layer 112b) on the line N is defined as c, and the length of the central portion 110C1 of the third resistance region 110C is defined as d. In this case, for example, 0.05≦d/c≦0.95 can be satisfied, and typically 0.1≦d/c≦0.9 can be satisfied.

Furthermore, with regard to the embodiment shown in FIG. 5, in a cross section perpendicular to the cell extension direction, the vertical width of the central portion 110C1 of the third resistance region 110C is defined as e, the vertical width of the left portion 110C2 of the third resistance region 110C is defined as f, and the vertical width of the right portion 110C3 of the third resistance region 110C is defined as g. In this case, for example, 0.05≦f/e≦0.95 and 0.05≦g/e≦0.95 can be satisfied, and typically 0.1≦f/e≦0.9 and 0.1≦g/e≦0.9 can be satisfied.

If the average electrical resistance per unit volume (1 ^cm3 ) of the first resistance region 110A _{is R1ave} , the average electrical resistance per unit volume (1 ^cm3 ) of the second resistance region 110B _{is R2ave} , and the average electrical resistance per unit volume (1 ^cm3 ) of the third resistance region 110C is _R3ave , then larger _R3ave / _R1ave and _R3ave / _R2ave are advantageous for suppressing temperature increases near the first electrode layer 112a and second electrode layer 112b, which are prone to excessive heat generation. However, if these ratios are made too large, the temperature near the central axis of the honeycomb structure portion will become relatively high, and this may cause cracks to occur.

Therefore, in a preferred embodiment, it is desirable that either or both of the relationships (1) and (2) are satisfied, and it is more desirable that both of the relationships (1) and (2) are satisfied.
1.2≦(R3 _ave /R1 _ave )≦4...(1)
1.2≦(R3 _ave /R2 _ave )≦4...(2)

In a more preferred embodiment, it is desirable that either or both of the relationships (3) and (4) are satisfied, and it is even more desirable that both of the relationships (3) and (4) are satisfied.
1.5≦(R3 _ave /R1 _ave )≦3.5...(3)
1.5≦(R3 _ave /R2 _ave )≦3.5...(4)

In an even more preferred embodiment, it is desirable that either or both of the relationships (5) and (6) are satisfied, and it is more desirable that both of the relationships (5) and (6) are satisfied.
2≦(R3 _ave /R1 _ave )≦3...(5)
2≦(R3 _ave /R2 _ave )≦3...(6)

The average electrical resistance per unit volume (1 ^cm3 ) in each resistance region can be calculated by determining the electrical resistance per unit volume (1 ^cm3 ) of all the square sections of the honeycomb structure that make up each resistance region and taking the arithmetic mean of these.

R1 _ave , R2 _ave , and R3 _ave may be set appropriately depending on the applied voltage, and there are no particular limitations. For example, R3 _ave can be set to 0.0001 to 20 Ω. For high voltages of 64 V or more, it can be set to 0.1 to 20 Ω, typically 0.5 to 15 Ω. For low voltages of less than 64 V, it can be set to 0.0001 to 1 Ω, typically 0.001 to 0.5 Ω.

The third resistance region 110C does not have a portion that contacts either the first electrode layer 112a or the second electrode layer 112b. From the viewpoint of improving heat generation uniformity, it is desirable that the third resistance region 110C be separated from the first electrode layer 112a and the second electrode layer 112b.
3, in a cross section perpendicular to the cell extension direction, a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b crosses the honeycomb structure section 110. The length (the distance between the surfaces of the outer walls, not including the electrode layers) of the third resistance region 110C is L. Preferably, the shortest distance D1 between the third resistance region 110C and the first electrode layer 112a is 0.02×L or more, and the shortest distance D2 between the third resistance region 110C and the second electrode layer 112b is 0.02×L or more. More preferably, the shortest distance D1 is 0.03×L or more, and the shortest distance D2 is 0.03×L or more. Even more preferably, the shortest distance D1 is 0.05×L or more, and the shortest distance D2 is 0.05×L or more.
The shortest distance D1 and the shortest distance D2 may be as long as the third resistance region 110C can be present, but from the viewpoint of uniform heat generation, it is more preferable that the shortest distance D1 is less than 0.5×L and the shortest distance D2 is less than 0.5×L. It is even more preferable that the shortest distance D1 is 0.45×L or less and the shortest distance D2 is 0.45×L or less, and it is particularly preferable that the shortest distance D1 is 0.3×L or less and the shortest distance D2 is 0.3×L or less.

Therefore, in a preferred embodiment, the relationships 0.02×L≦D1<0.5×L and 0.02×L≦D2<0.5×L are satisfied; in a more preferred embodiment, the relationships 0.03×L≦D1≦0.3×L and 0.03×L≦D2≦0.3×L are satisfied; and in an even more preferred embodiment, the relationships 0.05×L≦D1≦0.3×L and 0.05×L≦D2≦0.3×L are satisfied.

3 again, in a preferred embodiment, in a cross section perpendicular to the cell extension direction, the first resistance region 110A, the second resistance region 110B, and the third resistance region 110C are formed in line symmetry with a line N passing through the central axis O and perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. Also, in a preferred embodiment, in a cross section perpendicular to the cell extension direction, the first electrode layer 112a and the second electrode layer 112b are formed in line symmetry with a line N passing through the central axis O and perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. By forming the three resistance regions and the pair of electrode layers in line symmetry with the line N as the center of symmetry, an electrically heated carrier with the same heat generation performance can be obtained regardless of whether the first electrode layer 112a or the second electrode layer 112b is used as the anode (or whether it is used as the cathode). In this specification, the central axis O refers to the position of the center of gravity of the honeycomb structure in a cross section perpendicular to the cell extension direction.

As mentioned above, the slits may be provided to increase the electrical resistance in the third resistance region, but they can also be provided in cases where the honeycomb structure does not have a distinction between the first resistance region, the second resistance region, and the third resistance region. Figure 6 is a schematic diagram showing an example of the arrangement of multiple slits in a cross section perpendicular to the extension direction of the cells of an electrically heated carrier according to yet another embodiment of the present invention.

Referring to FIG. 6, the electrically heated carrier according to this embodiment is configured such that a portion of the partition wall 113 is missing in region 110D between a pair of opposing outer wall portions 114a, 114b on which neither the first electrode layer 112a nor the second electrode layer 112b is provided, and has one or more slits 120 extending in a direction intersecting an imaginary line 119 parallel to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. In a preferred embodiment, the angle φ (where 0°≦φ≦90°) formed by the one or more slits 120 with the imaginary line 119 is in the range of 80° to 90°.

The presence of the slits 120 reduces the electrical path, resulting in higher electrical resistance in the region where the slits 120 are provided (slit-forming region). Therefore, by providing the slits 120 in region 110D, which is sandwiched between a pair of outer wall portions 114a, 114b and on which neither the first electrode layer 112a nor the second electrode layer 112b is provided, it is possible to expect an effect similar to that achieved when the third resistance region 110C described above is provided. The slits 120 may be formed by removing only the partition wall 113, but the slits 120 may also be formed by removing not only the partition wall 113 but also the outer wall 114.

The slit formation region is preferably set to the same range as the extension of the third resistance region 110C. For example, as in the third resistance region 110C in the embodiment shown in Figure 3, multiple slits 120 can be provided within a region that extends in a band shape with a constant width in the vertical direction, crossing the cross section perpendicular to the extension direction of the cell from left to right.

Furthermore, as in the third resistance region 110C shown in FIG. 5, multiple slits 120 can be provided within a slit formation region defined by a center portion including the central axis O, a left side portion adjacent to the left of the center portion and narrower in the vertical direction than the center portion, and a right side portion adjacent to the right of the center portion and narrower in the vertical direction than the center portion. In the embodiment shown in FIG. 6, the vertical width of the slit formation region is narrower in the left side portion 110D2 and the right side portion 110D3 than in the center portion 110D1.

From the viewpoint of improving the uniformity of heat generation, it is desirable that the slit 120 be located away from the first electrode layer 112a and the second electrode layer 112b.
Specifically, referring to Figure 6, in a cross section perpendicular to the cell extension direction, if the length (the distance between the surfaces of the outer wall, not including the electrode layers) of a straight line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b across the honeycomb structure section 110 is L, it is preferable that the shortest distance D1 between the slit 120 and the first electrode layer 112a is 0.02 x L or more, and the shortest distance D2 between the slit 120 and the second electrode layer 112b is 0.02 x L or more. It is more preferable that the shortest distance D1 is 0.03 x L or more, and the shortest distance D2 is 0.03 x L or more. It is even more preferable that the shortest distance D1 is 0.05 x L or more, and the shortest distance D2 is 0.05 x L or more.
The shortest distance D1 and the shortest distance D2 may be made as long as the slits 120 are present, but from the viewpoint of uniform heat generation, it is more preferable that the shortest distance D1 is less than 0.5×L and the shortest distance D2 is less than 0.5×L. It is even more preferable that the shortest distance D1 is 0.45×L or less and the shortest distance D2 is 0.45×L or less, and it is particularly preferable that the shortest distance D1 is 0.3×L or less and the shortest distance D2 is 0.3×L or less.

Therefore, in a preferred embodiment, the relationships 0.02×L≦D1<0.5×L and 0.02×L≦D2<0.5×L are satisfied; in a more preferred embodiment, the relationships 0.03×L≦D1≦0.3×L and 0.03×L≦D2≦0.3×L are satisfied; and in an even more preferred embodiment, the relationships 0.05×L≦D1≦0.3×L and 0.05×L≦D2≦0.3×L are satisfied.

In a preferred embodiment, in a cross section perpendicular to the cell extension direction, the multiple slits 120 are formed in line symmetry with respect to a line N that passes through the central axis O and is perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. In a preferred embodiment, in a cross section perpendicular to the cell extension direction, the first electrode layer 112a and the second electrode layer 112b are formed in line symmetry with respect to a line N that passes through the central axis O and is perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. By forming the multiple slits 120 and the pair of electrode layers in line symmetry with respect to the line N, an electrically heated carrier with the same heat generation performance can be obtained regardless of whether the first electrode layer 112a or the second electrode layer 112b is used as the anode (or whether it is used as the cathode).

In the embodiment shown in Figure 6, when a cross section perpendicular to the cell extension direction is observed with the first electrode layer 112a positioned on the upper side and the second electrode layer 112b positioned on the lower side, the horizontal length of the center portion 110D1 of the slit formation region can be appropriately set taking into account the distribution of heat generation. However, in the slit formation region, current tends to flow inside the horizontal width of the first electrode layer 112a and the second electrode layer 112b, and the heat generation outside of that width tends to be small. For this reason, it is preferable to promote an increase in the amount of current outside the horizontal width of the first electrode layer 112a and the second electrode layer 112b. Therefore, in a preferred embodiment, the right end of the center portion 110D1 of the slit formation region is located to the right of the right edge of the first electrode layer 112a in the circumferential direction and to the right of the right edge of the second electrode layer 112b in the circumferential direction. Furthermore, the left end of the central portion 110D1 of the slit formation region is located to the left of the left end of the first electrode layer 112a in the circumferential direction, and is also located to the left of the left end of the second electrode layer 112b in the circumferential direction.

6 , in a cross section perpendicular to the cell extension direction, a line N is drawn that passes through the central axis O and is perpendicular to the line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b. In the direction in which line N extends, the length of the slit-forming region to the right of the right end of the circumferential direction of the first electrode layer 112a (second electrode layer 112b) is defined as a, and the length of the slit-forming region occupied by the center portion 110D1 is defined as b. In this case, the ratio b/a can be, for example, 0.05≦b/a≦0.95, and typically 0.1≦b/a≦0.9.
Similarly, in the direction in which the straight line N extends, the length of the slit-forming region to the left of the outer circumferential left end of the first electrode layer 112a (second electrode layer 112b) is defined as c, and the length of the slit-forming region occupied by the center portion 110D1 is defined as d. In this case, for example, 0.05≦d/c≦0.95 can be satisfied, and typically 0.1≦d/c≦0.9 can be satisfied.

Furthermore, with regard to the embodiment shown in FIG. 6, in a cross section perpendicular to the cell extension direction, the vertical width of the center 110D1 of the slit-forming region is defined as e, the vertical width of the left side 110D2 as f, and the vertical width of the right side 110D3 as g. In this case, for example, the relationships f/e and g/e can be set to 0.05≦f/e≦0.95 and 0.05≦g/e≦0.95, and typically, 0.1≦f/e≦0.9 and 0.1≦g/e≦0.9.

There is no particular lower limit to the length of each slit 120 in the longitudinal direction (left-right direction in Figure 6), but it is generally 2 mm or more. For reasons of strength (too many cell defects reduces strength and makes it impossible to withstand the stress during canning), the upper limit to the length of each slit 120 in the longitudinal direction is preferably 0.5 x L or less, more preferably 0.25 x L or less, and even more preferably 0.125 x L or less.

There is no particular lower limit to the length of each slit 120 in the short direction (vertical direction in Figure 6), but it is generally 1 mm or more. For reasons of strength (if there are many cell defects, the strength decreases and the slit 120 cannot withstand the stress during canning), the upper limit to the length of each slit 120 in the short direction is preferably 0.07 x L or less, more preferably 0.05 x L or less, and even more preferably 0.015 x L or less.

The arrangement of the multiple slits 120 is not limited, but it is preferable that they be arranged evenly in the slit formation region. Specifically, in a cross section perpendicular to the cell extension direction, the multiple slits 120 preferably form rows of slits 120 arranged at equal intervals in a direction perpendicular to a line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b (the horizontal direction in FIG. 6). One row of slits 120 can be composed of, for example, 1 to 27 slits. It is also preferable that the rows of multiple slits 120 be arranged at equal intervals in the vertical direction. The number of rows of slits 120 arranged in the vertical direction can be, for example, 1 to 50. In the embodiment shown in FIG. 6, five rows of slits 120 arranged at equal intervals in the horizontal direction are arranged at equal intervals in the vertical direction.

When arranging multiple rows of slits 120 in the vertical direction, it is preferable to arrange the slits 120 in a staggered (staggered) pattern. This ensures that when a voltage is applied between the first electrode layer 112a and the second electrode layer 112b, the current paths are reduced evenly in the slit formation region, improving heat generation uniformity. Furthermore, when arranging multiple rows of slits 120 in the vertical direction, it is more preferable to arrange the multiple slits 120 so that there are no current paths that linearly penetrate the slit formation region in the direction of a straight line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b (the vertical direction in Figure 6).

The material of the outer peripheral wall 114 and the partition walls 113 is not particularly limited as long as it is capable of generating heat through Joule heating when current is applied, and ceramics (particularly conductive ceramics) can be used alone or in combination. The material of the outer peripheral wall 114 and the partition walls 113 is not limited to, but can be one or more of oxide-based ceramics such as alumina, mullite, zirconia, and cordierite, or non-oxide-based ceramics such as silicon carbide, silicon nitride, and aluminum nitride. Silicon carbide-metal 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 outer peripheral wall 114 and the partition walls 113 be a silicon-silicon carbide composite or a material primarily composed of silicon carbide, and it is even more preferable that it be a silicon-silicon carbide composite or silicon carbide. When the material of the outer peripheral wall 114 and the partition walls 113 is said to be primarily composed of silicon-silicon carbide composite, it means that the outer peripheral wall 114 and the partition walls 113 each contain 90 mass% or more of the silicon-silicon carbide composite (total mass). Here, the silicon-silicon carbide composite contains silicon carbide particles as aggregate and silicon as a binder that bonds the silicon carbide particles, and it is preferable that multiple silicon carbide particles are bonded by the silicon so as to form pores between the silicon carbide particles. When the material of the outer peripheral wall 114 and the partition walls 113 is said to be primarily composed of silicon carbide, it means that the outer peripheral wall 114 and the partition walls 113 each contain 90 mass% or more of the silicon carbide (total mass).

When the outer peripheral wall 114 and the partition walls 113 contain a silicon-silicon carbide composite, the ratio of the "mass of silicon as a binder" contained in the outer peripheral wall 114 and the partition walls 113 to the sum of the "mass of silicon carbide particles as aggregate" contained in the outer peripheral wall 114 and the partition walls 113 and the "mass of silicon as a binder" contained in the outer peripheral wall 114 and the partition walls 113 is preferably 10 to 40 mass%, and more preferably 15 to 35 mass%. If it is 10 mass% or more, the strength of the outer peripheral wall 114 and the partition walls 113 is sufficiently maintained. If it is 40 mass% or less, the shape is more easily maintained during firing.

There are no restrictions on the shape of the cells 115 in a cross section perpendicular to their extension direction, but they are preferably rectangular, hexagonal, octagonal, or a combination of these. Of these, rectangular and hexagonal shapes are preferred. By using such a cell shape, pressure loss when exhaust gas flows through the honeycomb structure section 110 is reduced, resulting in excellent catalyst purification performance.

The cells 115 may extend from one end face 116 to the other end face 118. Alternatively, the cells 115 may be arranged alternately adjacent to each other with the partition wall 113 in between, with first cells having one end face 116 plugged and the other end face 118 having an opening, and second cells having one end face 116 open and the other end face 118 plugged.

The thickness of the partition walls 113 that define the cells 115 is preferably 0.1 to 0.3 mm, and more preferably 0.1 to 0.2 mm. Having a thickness of 0.1 mm or more for the partition walls 113 can prevent a decrease in the strength of the honeycomb structure section 110. Having a thickness of 0.3 mm or less for the partition walls 113 can prevent an increase in pressure loss when exhaust gas flows through the honeycomb structure section 110 when the honeycomb structure section 110 is used as a catalyst carrier to support the catalyst. In the present invention, the thickness of the partition walls 113 is defined as the length of the portion of the line segment connecting the centers of gravity of adjacent cells 115 that passes through the partition walls 113 in a cross section perpendicular to the extension direction of the cells 115.

The honeycomb structure section 110 preferably has a cell density of 40 to 150 cells/ ^cm2 , more preferably 70 to 100 cells/ ^cm2 , in a cross section perpendicular to the extension direction of the cells 115. By setting the cell density within this range, it is possible to improve the purification performance of the catalyst while reducing the pressure loss when exhaust gas is passed through the honeycomb structure section 110. When the cell density is 40 cells/ ^cm2 or more, a sufficient catalyst support area is ensured. When the cell density is 150 cells/ ^cm2 or less, when the honeycomb structure section 110 is used as a catalyst support to support a catalyst, excessive pressure loss when exhaust gas is passed through the honeycomb structure section 110 is prevented. The cell density is a value obtained by dividing the number of cells by the area of one end face of the honeycomb structure section 110 located on the inner peripheral side of the outer peripheral wall 114.

The partition walls 113 may be dense, such as in the form of Si-impregnated SiC, but are preferably porous. The porosity of the partition walls 113 is preferably 35 to 60%, and more preferably 35 to 45%. A porosity of 35% or more makes it easier to suppress deformation during firing. A porosity of 60% or less ensures that the strength of the honeycomb structure section 110 is sufficiently maintained. The porosity is a value measured using a mercury porosimeter. Note that a dense structure refers to a porosity of 5% or less.

The average pore diameter of the partition walls 113 is preferably 2 to 15 μm, and more preferably 4 to 8 μm. If the average pore diameter is 2 μm or more, the volume resistivity is prevented from becoming too large. If the average pore diameter is 15 μm or less, the volume resistivity is prevented from becoming too small. The average pore diameter is a value measured using a mercury porosimeter.

(1-2. Electrode layer)
The electrode layers (112a, 112b) will be described with reference to FIGS. 1A and 1B . A first electrode layer 112a is provided in a strip shape on the surface of the outer peripheral wall 114 in the extension direction of the cells 115. Furthermore, a second electrode layer 112b is provided in a strip shape on the surface of the outer peripheral wall 114 in the extension direction of the cells 115, facing the first electrode layer 112a across the central axis O of the honeycomb structure section 110. In general, the first electrode layer 112a and the second electrode layer 112b have a lower volume resistivity than the outer peripheral wall 114. Therefore, by disposing the pair of electrode layers 112a, 112b on the surface of the outer peripheral wall 114, current is more likely to spread in the circumferential direction of the honeycomb structure section 110 and in the extension direction of the cells 115, thereby improving the uniform heat generation of the honeycomb structure section 110. Specifically, in a cross section perpendicular to the extension direction of the cell 115, the angle θ (0°≦θ≦180°) formed by two line segments extending from the circumferential centers of each of the pair of electrode layers 112a, 112b to the central axis O of the honeycomb structure section 110 is preferably 150°≦θ≦180°, more preferably 160°≦θ≦180°, even more preferably 170°≦θ≦180°, and most preferably 180°.

While there are no particular restrictions on the formation area of the electrode layers 112a and 112b, from the perspective of improving the uniform heat generation of the honeycomb structure section 110, it is preferable that the electrode layers 112a and 112b each extend in a strip-like manner on the outer surface of the outer wall 114 in the circumferential direction of the honeycomb structure section 110 and in the extension direction of the cells 115. Specifically, in a cross section perpendicular to the extension direction of the cells 115, the central angle α formed by two line segments connecting the circumferential ends of each electrode layer 112a and 112b to the central axis O is preferably 30° or greater, more preferably 40° or greater, and even more preferably 60° or greater, from the perspective of spreading the current circumferentially and improving uniform heat generation. However, if the central angle α is made too large, less current will pass through the interior of the honeycomb structure section 110, and more current will pass near the outer wall 114. Therefore, from the viewpoint of uniform heat generation in the honeycomb structure section 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, 112b each extend over 80% or more of the length between both end faces of the honeycomb structure section 110, preferably over 90% or more, and more preferably over the entire length. The electrode layers 112a, 112b may be composed of a single layer, or may have a laminated structure in which multiple layers are stacked.

The thickness of the electrode layers 112a, 112b is preferably 0.01 to 5 mm, and more preferably 0.01 to 3 mm. Setting the thickness within this range enhances uniform heat generation. When the thickness of the electrode layers 112a, 112b is 0.01 mm or more, electrical resistance is appropriately controlled, allowing for more uniform heat generation. When the thickness is 5 mm or less, the risk of breakage during canning is reduced. The thickness of the electrode layers 112a, 112b is defined as the thickness in the direction normal to the tangent to the outer surface of the electrode layers 112a, 112b at the measurement point when the location of the electrode layers 112a, 112b where the thickness is to be measured is observed in a cross section perpendicular to the extension direction of the cell 115.

By making the volume resistivity of the electrode layers 112a, 112b lower than that of the partition walls 113 and the outer peripheral wall 114, electricity flows preferentially through the electrode layers 112a, 112b, and when energized, electricity spreads more easily in the circumferential direction of the honeycomb structure section 110 and in the extension direction of the cells 115. The volume resistivity of the electrode layers 112a, 112b is preferably 1/10 or less of the volume resistivity of the partition walls 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, 112b, causing uneven heat generation in the honeycomb structure section 110. Therefore, the volume resistivity of the electrode layers 112a, 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 walls 113 and outer peripheral wall 114. In the present invention, the volume resistivities of the electrode layers, partition walls, and outer peripheral wall are values measured at 25°C using the four-terminal method.

The material of the electrode layers 112a, 112b is not limited to, but may be a composite (cermet) of metal and ceramic (especially conductive ceramic). Examples of metals include, for example, Cr, Fe, Co, Ni, Si, or Ti, or alloys containing at least one metal selected from these metals. Examples of ceramics include, but are not limited to, silicon carbide (SiC), as well as metal compounds such as metal silicides, such as tantalum silicide (TaSi ₂ ) and chromium silicide (CrSi ₂ ). Specific examples of composites (cermets) of metal and ceramic include composites of metal silicon and silicon carbide, composites of metal silicides, such as tantalum silicide or chromium silicide, and composites in which one or more insulating ceramics, such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride, are added to one or more of the above metals to reduce thermal expansion. As the material for the electrode layers 112a, 112b, among the various metals and ceramics mentioned above, a composite material of metal silicon and silicon carbide is preferred because it can be fired simultaneously with the partition walls and the outer peripheral wall, which contributes to simplifying the manufacturing process.

(1-3. Metal terminal)
1A and 1B , the electrically heated carrier 100 may include at least one first metal terminal 130a electrically connected to the first electrode layer 112a and at least one second metal terminal 130b electrically connected to the second electrode layer 112b. The first electrode layer 112a and the first metal terminal 130a may be directly bonded to each other, or one or more base layers (not shown) may be provided between them to reduce the difference in thermal expansion and improve the bonding reliability. Similarly, the second electrode layer 112b and the second metal terminal 130b may be directly bonded to each other, or one or more base layers may be provided between them to reduce the difference in thermal expansion and improve the bonding reliability.

When a voltage is applied to the honeycomb structure section 110 via the metal terminals 130a and 130b, electricity flows and Joule heat is generated in the honeycomb structure section 110. Therefore, the honeycomb structure section 110 can also be suitably used as a heater. This makes it possible to improve the uniform heat generation of the honeycomb structure section 110. The applied voltage is preferably 12 to 900 V, and more preferably 48 to 600 V, but the applied voltage can be changed as appropriate.

There are no particular restrictions on the method for joining the metal terminals 130a, 130b to the electrode layers 112a, 112b (or the base layer, if provided), but examples include welding, thermal spraying, and brazing. Of these, welding and thermal spraying are preferred because they cause minimal deterioration at the joint even when heated to 800°C or higher.

There are no particular restrictions on the material of the metal terminals 130a and 130b, as long as it is metal, and simple metals and alloys can be used. However, from the standpoint of corrosion resistance, volume resistivity, and linear expansion coefficient, it is preferable to use an alloy containing at least one element selected from the group consisting of Cr, Fe, Co, Ni, and Ti, with stainless steel and Fe-Ni alloys being more preferred.

(2. Manufacturing method)
Next, a method for manufacturing an electrically heated carrier according to one embodiment of the present invention will be described by way of example. The electrically heated carrier can be manufactured by a manufacturing method including a step A1 of obtaining a honeycomb formed body, a step A2 of obtaining an unfired honeycomb structure with an electrode layer forming paste, a step A3 of firing the unfired honeycomb structure with the electrode layer forming paste to obtain a honeycomb structure, and a step A4 of joining metal terminals to the electrode layers of the honeycomb structure.

(Step A1)
Step A1 is a step of forming a honeycomb formed body, which is a precursor of the honeycomb structure. The honeycomb formed body can be produced in accordance with a method for producing a honeycomb formed body in a known honeycomb structure manufacturing method. For example, first, a forming raw material is produced by adding metal silicon powder (metal silicon), a binder, a surfactant, a pore-forming material, water, etc. to silicon carbide powder (silicon carbide). It is preferable that the mass of the metal silicon powder is 10 to 40 mass% relative to the total mass of the silicon carbide powder and the metal silicon powder. The average particle diameter of the silicon carbide particles in the silicon carbide powder is preferably 3 to 50 μm, more preferably 3 to 40 μm. The average particle diameter of the metal silicon particles in the metal silicon powder is preferably 2 to 35 μm. The average particle diameter of the silicon carbide particles and the metal silicon particles refers to the arithmetic mean diameter based on volume when measuring the particle size frequency distribution by laser diffraction. The silicon carbide particles are fine particles of silicon carbide that constitute silicon carbide powder, and the metallic silicon particles are fine particles of metallic silicon that constitute metallic silicon powder. Note that this is the blending of the forming raw materials when the material of the honeycomb structure is a silicon-silicon carbide composite material, and when the material of the honeycomb structure is silicon carbide, metallic silicon is not added.

Examples of binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol. Among these, it is preferable to use a combination of methyl cellulose and hydroxypropoxyl cellulose. The binder content is preferably 2.0 to 10.0 parts by mass when the total mass of the silicon carbide powder and metallic silicon powder is 100 parts by mass.

Surfactants that can be used include ethylene glycol, dextrin, fatty acid soap, polyalcohol, etc. These may be used alone or in combination of two or more. The surfactant content is preferably 0.1 to 2.0 parts by mass when the total mass of the silicon carbide powder and metallic silicon powder is 100 parts by mass.

The pore-forming material is not particularly limited as long as it forms pores after firing, and examples include graphite, starch, foamed resin, water-absorbent 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 the 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 on a volume basis when the particle size frequency distribution is measured using laser diffraction. When the pore-forming material is a water-absorbent resin, the average particle diameter of the pore-forming material refers to the average particle diameter after absorbing water.

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

Next, the obtained molding raw materials are kneaded to form a clay, which is then extruded to produce a honeycomb molded body having an outer wall and partition walls. A die having the desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used during extrusion molding. When providing slits by removing a portion of the partition walls 113 in the third resistance region 110C, the partition walls can be removed by closing a portion of the die corresponding to the portion where the partition walls are to be removed. Next, the obtained honeycomb molded body is preferably dried. If the length of the honeycomb molded body in the central axis direction is not the desired length, both ends of the honeycomb molded body can be cut to the desired length. The dried honeycomb molded body is called a dried honeycomb body.

As a variation of step A1, the honeycomb formed body may be fired first. That is, in this variation, the honeycomb formed body is fired to produce a honeycomb fired body, and step A2 is then performed on the honeycomb fired body.

(Step A2)
Step A2 is a step of applying an electrode layer forming paste to the side surface of the honeycomb formed body to obtain an unfired honeycomb structure with the electrode layer forming paste. The electrode layer forming paste can be formed by appropriately adding various additives to raw material powders (metal powders, ceramic powders, etc.) blended according to the required characteristics of the electrode layer, and kneading the mixture. The average particle diameter of the raw material powder is not limited, but is preferably, for example, 5 to 50 μm, and more preferably 10 to 30 μm. The average particle diameter of the raw material powder refers to the arithmetic mean diameter on a volume basis when the particle size frequency distribution is measured by laser diffraction.

Next, the obtained electrode layer forming paste is applied to the required locations on the side of a honeycomb formed body (typically a dried honeycomb body) to obtain an unfired honeycomb structure with electrode layer forming paste. The method of preparing the electrode layer forming paste and the method of applying the electrode layer forming paste to the honeycomb formed body can be carried out in accordance with known honeycomb structure manufacturing methods. However, in order to give the electrode layer a lower volume resistivity than the outer wall and partition walls, the metal content can be made higher than that of the outer wall and partition walls, or the particle size of the metal particles in the raw material powder can be made smaller.

(Step A3)
Step A3 is a step of obtaining a honeycomb structure by firing the unfired honeycomb structure with the electrode layer forming paste. The unfired honeycomb structure with the electrode layer forming paste may be dried before firing. Furthermore, degreasing may be performed before firing to remove binders and the like. Firing conditions vary depending on the material of the honeycomb structure, but preferably involve heating at 1400 to 1500°C for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. Furthermore, after firing, it is preferable to perform oxidation treatment at 1200 to 1350°C for 1 to 10 hours to improve durability. The degreasing and firing methods are not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like.

(Step A4)
In step A4, a metal terminal is bonded onto the electrode layer of the honeycomb structure by a bonding method such as welding, thermal spraying, or brazing.

A suitable catalyst may be supported on the honeycomb structure depending on the application. One example of a method for supporting a catalyst on a honeycomb structure is to introduce a catalyst slurry into the cells using a conventional suction method, allow it to adhere to the surfaces and pores of the partition walls, and then subject it to high-temperature treatment to bake the catalyst contained in the catalyst slurry onto the partition walls and support it.

(3. Exhaust gas purification device)
The electrically heated carrier according to the embodiment of the present invention can be used in an exhaust gas purification device. The exhaust gas purification device has an electrically heated carrier and a cylindrical metal tube that houses the electrically heated carrier. In the exhaust gas purification device, the electrically heated carrier can be installed midway through an exhaust gas flow path for flowing exhaust gas from an engine. The metal tube can be a metallic cylindrical member that houses the electrically heated carrier.

The following examples are provided to provide a better understanding of the present invention and its advantages, but the present invention is not limited to these examples.

<I. Test Numbers 1 to 8>
(1. Preparation of cylindrical clay)
A ceramic raw material was prepared by mixing silicon carbide (SiC) powder and metallic silicon (Si) powder in a mass ratio of 80:20. Hydroxypropyl methylcellulose as a binder, a water-absorbent resin as a pore-forming material, and water were added to the ceramic raw material to form a molding raw material. The molding raw material was then kneaded using a vacuum kneader to prepare a cylindrical clay. The binder content was 7 parts by mass when the total of the silicon carbide (SiC) powder and metallic silicon (Si) powder was 100 parts by mass. The pore-forming material content was 3 parts by mass when the total of the silicon carbide (SiC) powder and metallic silicon (Si) powder was 100 parts by mass. The water content was 42 parts by mass when the total of the silicon carbide (SiC) powder and metallic silicon (Si) powder was 100 parts by mass. The average particle diameter of the silicon carbide powder was 20 μm, and the average particle diameter of the metallic silicon powder was 6 μm. The average particle size of the pore-forming material was 20 μm. The average particle sizes of the silicon carbide powder, the metallic silicon powder, and the pore-forming material refer to the arithmetic mean diameter on a volume basis when the particle size frequency distribution is measured by laser diffraction.

(2. Preparation of dried honeycomb body)
The obtained cylindrical clay was molded using an extrusion molding machine with a grid-patterned die structure to obtain a cylindrical honeycomb molded body in which each cell had a hexagonal shape in a cross section perpendicular to the cell flow direction. During extrusion molding, the die was designed so that all partition walls had a uniform thickness in Test No. 1. Meanwhile, for Test Nos. 2 to 8, when a cross section perpendicular to the cell extension direction was observed with the first electrode layer 112a positioned on the upper side and the second electrode layer 112b positioned on the lower side, the thickness of the partition walls in the locations where the third resistance region 110C was to be formed was made thinner than the thickness of the partition walls in the locations where the first resistance region 110A and the second resistance region 110B were to be formed, so that a strip-shaped third resistance region 110C with a uniform width in the vertical direction was formed across the cross section, as shown in FIG. 3 . The degree of thinning varied depending on the test number. This honeycomb molded body was dried by high frequency dielectric heating, and then dried at 120° C. for 2 hours using a hot air dryer, and both end faces were cut off by a predetermined amount to prepare a dried honeycomb body.

(3. Preparation of electrode layer forming paste)
Metallic silicon (Si) powder, silicon carbide (SiC) powder, methyl cellulose, glycerin, and water were mixed using a planetary centrifugal mixer to prepare an electrode layer-forming paste. The Si powder and SiC powder were blended in a volume ratio of Si powder:SiC powder = 40:60. Furthermore, when the total of the Si powder and SiC powder was 100 parts by mass, the methyl cellulose was 0.5 parts by mass, the glycerin was 10 parts by mass, and the water was 38 parts by mass. The average particle diameter of the metallic silicon powder was 6 μm. The average particle diameter of the silicon carbide powder was 35 μm. These average particle diameters refer to the arithmetic mean diameter based on volume when the particle size frequency distribution was measured by laser diffraction.

(4. Application of electrode layer forming paste)
The electrode layer forming paste was applied to two locations on the outer surface of the peripheral wall of the dried honeycomb body using a curved surface printing machine, facing each other across the central axis. Each application location was formed in a strip shape over the entire length between both end faces of the dried honeycomb body (angle θ = 180°, central angle α = 100°).

(5. Firing)
The dried honeycomb body with the electrode layer forming paste was dried at 120°C and then degreased in an air atmosphere at 550°C for 3 hours. Next, the degreased dried honeycomb body with the electrode layer forming paste was fired and then subjected to an oxidation treatment to produce a honeycomb structure with an electrode layer. The firing was performed in an argon atmosphere at 1450°C for 2 hours. The oxidation treatment was performed in air at 1300°C for 1 hour. Note that the number of honeycomb structures with electrode layers for each test number required for the following evaluations was produced.

The honeycomb structure with electrode layers obtained under the above manufacturing conditions had circular end faces with a diameter of 93 mm (excluding the electrode layers) and a height (length in the cell extension direction) of 65 mm. The cell density was 90 cells/ ^cm2 , the outer wall thickness was 300 μm, the partition wall porosity was 45%, and the partition wall average pore diameter was 8.6 μm. The electrode layer thickness was 0.3 mm. Table 1 also shows the partition wall thickness for each resistance region for each test number.

The arrangement of the resistance regions in the honeycomb structure portion of the electrode layer-attached honeycomb structures according to test numbers 2 to 8, obtained under the above manufacturing conditions, was L = 93 mm, D1 = 0.05 × L (4.89 mm), and D2 = 0.05 × L (4.89 mm). The definitions of L, D1, and D2 are as described above. The first resistance region 110A, second resistance region 110B, and third resistance region 110C were formed symmetrically with respect to a line N that passes through the central axis O and is perpendicular to a line L connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b.

In Test No. 1, the electrical resistance per unit volume (1 cm ³ ) within the honeycomb structure was substantially constant, so a 3 cm ³ rectangular parallelepiped sample was taken from any location within the honeycomb structure and measured at room temperature (25°C) using the four-terminal method. In Test Nos. 2 to 8, the electrical resistance per unit volume (1 cm ³ ) within the first resistance region 110A, second resistance region 110B, and third resistance region 110C was substantially constant within each region, so a 3 cm ³ rectangular parallelepiped sample was taken from any location within each resistance region of the honeycomb structure and measured at room temperature (25°C) using the four-terminal method. The results are shown in Table 1. The electrical resistance values listed in Table 1 correspond to the average electrical resistance per unit volume (1 cm ³ ) within each resistance region.

(6. Simulation of Temperature Distribution)
For the honeycomb structure obtained under the above manufacturing conditions, a voltage of 7 kW was applied to the center of each surface of a pair of electrode layers for 30 seconds. The temperature distribution at the center of the honeycomb structure in the cell extension direction, in a cross section perpendicular to the cell extension direction, was simulated using commercially available finite element CAE analysis software. Temperatures were measured at five locations, _t1 to _t5 , as shown in Figure 3. Since the first resistance region 110A, the second resistance region 110B, and the third resistance region 110C are formed in line symmetry with respect to the line N, the temperature distribution in the lower half of Figure 3 is not shown, but appears generally line symmetrical to the upper half. The results are shown in Table 2.

(7. Crack Evaluation)
For the honeycomb structures obtained under the above manufacturing conditions, a voltage of 7 kW was applied to the center of each surface of a pair of electrode layers for 30 seconds, and then the outer wall and the electrode layers were visually evaluated for cracks. The evaluation of the cracks was based on the following criteria. The results are shown in Table 2.
A: No cracks B: Minor cracks (no cracks were observed from the current distribution, and the cracks were at a level that did not affect current-carrying performance)
C: Cracks present (cracks can be seen from the distribution of current flow, and are at a level that affects current flow performance)

<II. Test Nos. 9 to 12>
Cylindrical honeycomb structures were obtained in the same manner as in Test No. 3, except that the length (L) of the line connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b across the honeycomb structure portion 110, the formation area of the electrode layers (central angle α), and the arrangements (D1 and D2) of the first resistance region 110A, the second resistance region 110B, and the third resistance region 110C were changed as shown in Table 2. Temperature distribution simulation and crack evaluation were performed on the obtained honeycomb structures in the same manner as in Test No. 3. The results are shown in Table 2.

<III. Test No. 13>
(1. Preparation of cylindrical clay)
Cylindrical clay bodies were prepared in the same manner as in Test No. 1, except for the diameter.

(2. Preparation of dried honeycomb body)
The obtained cylindrical clay was molded using an extruder with a grid-like die structure to obtain a cylindrical honeycomb molded body in which each cell had a hexagonal shape in a cross section perpendicular to the cell flow direction. During extrusion molding, when a cross section perpendicular to the cell extension direction is observed with the first electrode layer 112a positioned on the upper side and the second electrode layer 112b positioned on the lower side, the thickness of the partition walls in the location where the third resistance region 110C was to be formed was made thinner than the thickness of the partition walls in the locations where the first resistance region 110A and the second resistance region 110B were to be formed so that a strip-shaped third resistance region 110C with a constant width in the up-down direction and extending horizontally across the cross section perpendicular to the cell extension direction, as shown in FIG. 4, was formed. Furthermore, the thickness of the partition walls in the third resistance region 110C was adjusted so that the following three regions were formed within the third resistance region 110C.
A central portion 110C1 including the central axis O of the honeycomb structure portion 110.
A left side portion 110C2 that is adjacent to the left end of the central portion 110C1 and extends to the left end of the third resistance region 110C, and has a lower electrical resistance per unit volume (1 cm ³ ) than the central portion 110C1.
A right side portion 110C3 that is adjacent to the right end of the central portion 110C1 and extends to the right end of the third resistance region 110C, and has a lower electrical resistance per unit volume (1 cm ³ ) than the central portion 110C1.

This honeycomb molded body was dried using high-frequency dielectric heating, then dried at 120°C for 2 hours using a hot air dryer, and both end faces were cut off to a specified length to produce a dried honeycomb body.

(3. Preparation of electrode layer forming paste)
An electrode layer forming paste similar to that of Test No. 1 was prepared.

(4. Application of electrode layer forming paste)
The electrode layer forming paste was applied to two locations on the outer surface of the outer wall of the dried honeycomb body, facing each other across the central axis, using a curved surface printing machine. Each application location was formed in a strip shape over the entire length between both end faces of the dried honeycomb body (angle θ = 180°, central angle α = 93°).

(5. Firing)
The dried honeycomb body with the electrode layer forming paste was dried at 120°C and then degreased in an air atmosphere at 550°C for 3 hours. Next, the degreased dried honeycomb body with the electrode layer forming paste was fired and then subjected to an oxidation treatment to produce a honeycomb structure with an electrode layer. The firing was performed in an argon atmosphere at 1450°C for 2 hours. The oxidation treatment was performed in air at 1300°C for 1 hour. Note that the number of honeycomb structures with electrode layers for each test number required for the following evaluations was produced.

The honeycomb structure with electrode layers obtained under the above manufacturing conditions had circular end faces with a diameter of 118 mm (excluding the electrode layers) and a height (length in the cell extension direction) of 65 mm. The cell density was 90 cells/ ^cm2 , the outer wall thickness was 300 μm, the partition wall porosity was 45%, and the partition wall average pore diameter was 8.6 μm. The electrode layer thickness was 0.3 mm. Table 1 shows the partition wall thickness for each resistance region.

The arrangement of the resistance regions in the honeycomb structure portion of the honeycomb structure with electrode layers obtained under the above manufacturing conditions was as follows: L = 118 mm, D1 = 0.05 × L (5.61 mm), D2 = 0.05 × L (5.61 mm), b/a = 0.14, and d/c = 0.14. The definitions of L, D1, D2, b/a, and d/c are as described above. The first resistance region 110A, second resistance region 110B, and third resistance region 110C were formed symmetrically with respect to a line N that passes through the central axis O and is perpendicular to a line L connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b.

Because the electrical resistance per unit volume (1 ^cm3 ) in the first resistance region 110A and the second resistance region 110B is substantially constant within each region, a 3 ^cm3 rectangular parallelepiped sample was taken from any location in each resistance region of the honeycomb structure and measured at room temperature (25°C) using the four-terminal method. The third resistance region 110C is divided into three regions: a central region 110C1, a left region 110C2, and a right region 110C3. The electrical resistance per unit volume (1 ^cm3 ) in each region is substantially constant. Therefore, the electrical resistance per unit volume (1 ^cm3 ) was determined by taking a ³ cm3 rectangular parallelepiped sample from any location in the central region 110C1, the left region 110C2, and the right region 110C3 and measuring it at room temperature (25°C) using the four-terminal method. The results are shown in Table 1. The electrical resistance values shown in Table 1 correspond to the average electrical resistance per unit volume (1 cm ³ ) in each resistance region.

(6. Characterization)
For the obtained honeycomb structure, a simulation of temperature distribution was carried out in the same manner as in Test No. 1. The results are shown in Table 2.

<IV. Test No. 14>
(1. Preparation of cylindrical clay)
Cylindrical clay bodies were prepared in the same manner as in Test No. 1, except for the diameter.

(2. Preparation of dried honeycomb body)
The obtained cylindrical clay was molded using an extruder with a grid-like die structure to obtain a cylindrical honeycomb molded body in which each cell had a hexagonal shape in a cross section perpendicular to the cell flow direction. During extrusion molding, when a cross section perpendicular to the cell extension direction is observed with the first electrode layer 112a positioned on the upper side and the second electrode layer 112b positioned on the lower side, the thickness of the partition walls in the locations where the third resistance region 110C was to be formed was made thinner than the thickness of the partition walls in the locations where the first resistance region 110A and the second resistance region 110B were to be formed, so that the third resistance region 110C would be formed across the cross section perpendicular to the cell extension direction and have a varying width in the vertical direction, as shown in Figure 5. In addition, the arrangement of the third resistance region 110C was adjusted so that the following three regions were formed within the third resistance region 110C.
A central portion 110C1 including the central axis O of the honeycomb structure portion 110.
A left side portion 110C2 that is adjacent to the left end of the center portion 110C1, extends to the left end of the third resistance region 110C, and has a narrower width in the up-down direction than the center portion 110C1.
A right side portion 110C3 that is adjacent to the right end of the central portion 110C1, extends to the right end of the third resistance region 110C, and has a narrower width in the up-down direction than the central portion 110C1.

This honeycomb molded body was dried using high-frequency dielectric heating, then dried at 120°C for 2 hours using a hot air dryer, and both end faces were cut off to a specified length to produce a dried honeycomb body.

(3. Preparation of electrode layer forming paste)
An electrode layer forming paste similar to that of Test No. 1 was prepared.

(4. Application of electrode layer forming paste)
The electrode layer forming paste was applied to two locations on the outer surface of the outer wall of the dried honeycomb body, facing each other across the central axis, using a curved surface printing machine. Each application location was formed in a strip shape over the entire length between both end faces of the dried honeycomb body (angle θ = 180°, central angle α = 93°).

(5. Firing)
The dried honeycomb body with the electrode layer forming paste was dried at 120°C and then degreased in an air atmosphere at 550°C for 3 hours. Next, the degreased dried honeycomb body with the electrode layer forming paste was fired and then subjected to an oxidation treatment to produce a honeycomb structure with an electrode layer. The firing was performed in an argon atmosphere at 1450°C for 2 hours. The oxidation treatment was performed in air at 1300°C for 1 hour. Note that the number of honeycomb structures with electrode layers for each test number required for the following evaluations was produced.

The honeycomb structure with electrode layers obtained under the above manufacturing conditions had circular end faces with a diameter of 118 mm (excluding the electrode layers) and a height (length in the cell extension direction) of 65 mm. The cell density was 90 cells/ ^cm2 , the outer wall thickness was 300 μm, the partition wall porosity was 45%, and the partition wall average pore diameter was 8.6 μm. The electrode layer thickness was 0.3 mm. Table 1 shows the partition wall thickness for each resistance region.

The arrangement of the resistance regions in the honeycomb structure portion of the honeycomb structure with electrode layers obtained under the above manufacturing conditions was as follows: L = 118 mm, D1 = 0.05 × L (5.61 mm), D2 = 0.05 × L (5.61 mm), b/a = 0.14, d/c = 0.14, f/e = 0.71, and g/e = 0.71. The definitions of L, D1, D2, b/a, d/c, f/e, and g/e are as described above. The first resistance region 110A, second resistance region 110B, and third resistance region 110C were formed symmetrically with respect to a line N that passes through the central axis O and is perpendicular to a line L connecting the circumferential center of the first electrode layer 112a and the circumferential center of the second electrode layer 112b.

Since the electrical resistance per unit volume (1 ^cm3 ) in the first resistance region 110A, the second resistance region 110B, and the third resistance region 110C is substantially constant within each region, a rectangular parallelepiped sample of 3 ^cm3 was taken from any location in each resistance region of the honeycomb structure and measured at room temperature (25°C) using the four-terminal method. The results are shown in Table 1.

(6. Characterization)
For the obtained honeycomb structure, a simulation of temperature distribution was carried out in the same manner as in Test No. 1. The results are shown in Table 2.

<V. Consideration>
As can be seen from the results in Tables 1 and 2, by using the honeycomb structure (electrically heated carrier) according to the embodiment of the present invention (Test Nos. 2 to 14), the generation of cracks was suppressed while the heat generation uniformity was improved. Furthermore, by comparing Test Nos. 3, 9 to 11 with Test No. 12, it can be seen that by optimizing the arrangement of the first resistance region, the second resistance region, and the third resistance region, the generation of cracks was suppressed while the heat generation uniformity was significantly improved.

100: Electrically heated carrier 110: Honeycomb structure portion 110A: First resistance region 110B: Second resistance region 110C: Third resistance region 110C1: Center portion 110C2: Left portion 110C3: Right portion 110D1: Center portion 110D2: Left portion 110D3: Right portion 112a: First electrode layer 112b: Second electrode layer 113: Partition wall 114: Outer wall 115: Cell 116: End surface 118: End surface 119: Virtual line 130a: First metal terminal 130b: Second metal terminal

Claims (10)

a conductive honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells that form flow paths from one end face to the other end face;
a first electrode layer provided in a strip shape on the surface of the outer peripheral wall in the extending direction of the cell; and
a second electrode layer provided in a strip shape on the surface of the outer peripheral wall in the extending direction of the cells, the second electrode layer being provided so as to face the first electrode layer across the central axis of the honeycomb structure section;
Equipped with
In a cross section perpendicular to the cell extension direction, the honeycomb structure portion has
a first resistive region having a contact to the first electrode layer;
a second resistive region having a contact to the second electrode layer; and
a third resistance region that does not contact either the first electrode layer or the second electrode layer and crosses the cross section so as to be sandwiched between the first resistance region and the second resistance region;
the third resistance region has a higher electrical resistance per unit volume (1 cm ³ ) than ^the first resistance region and the second resistance region;
Electrically heated carrier. In a cross section perpendicular to the extension direction of the cell, the shortest distance between the third resistance region and the first electrode layer is 0.02×L or more, and the shortest distance between the third resistance region and the second electrode layer is 0.02×L or more.
(The above L indicates the length of a straight line connecting the center of the first electrode layer in the circumferential direction and the center of the second electrode layer in the circumferential direction, which crosses the honeycomb structure section.)
2. The electrically heated carrier according to claim 1. An electrically heated carrier as described in claim 1 or 2, wherein when the average electrical resistance per unit volume (1 ^cm3 ) of the first resistance region _is R1 _ave , the average electrical resistance per unit volume (1 ^cm3 ) of the second resistance region is R2 _ave , and the average electrical resistance per unit volume (1 ^cm3 ) of the third resistance region is R3 ave, either or both of the relationships (1) and (2) hold.
1.2≦(R3 _ave /R1 _ave )≦4...(1)
1.2≦(R3 _ave /R2 _ave )≦4...(2) When a cross section perpendicular to the extending direction of the cell is observed with the first electrode layer on the upper side and the second electrode layer on the lower side, the third resistance region has
- a center portion including a central axis of the honeycomb structure portion,
a left side portion adjacent to the left end of the center portion and extending to the left end of the third resistance region, and having a lower electrical resistance per unit volume (1 cm ³ ) than the center portion; and a right side portion adjacent to the right end of the center portion and extending to the right end of the third resistance region, and having a lower electrical resistance per unit volume (1 cm ³ ) than the center portion.
It is divided into three areas:
The electrically heated carrier according to any one of claims 1 to 3. When a cross section perpendicular to the extending direction of the cell is observed with the first electrode layer on the upper side and the second electrode layer on the lower side, the third resistance region has
- a center portion including a central axis of the honeycomb structure portion,
a left side portion adjacent to the left end of the center portion, extending to the left end of the third resistance region, and having a narrower width in the vertical direction than the center portion; and a right side portion adjacent to the right end of the center portion, extending to the right end of the third resistance region, and having a narrower width in the vertical direction than the center portion.
It is divided into three areas:
The electrically heated carrier according to any one of claims 1 to 4. a right end of a center portion of the third resistance region is located to the right of a right end of the first electrode layer in a circumferential direction and is located to the right of a right end of the second electrode layer in a circumferential direction;
a left end of the center of the third resistance region is located to the left of the left end of the first electrode layer in the circumferential direction and is located to the left of the left end of the second electrode layer in the circumferential direction;
6. An electrically heated carrier according to claim 4 or 5. An electrically heated carrier according to any one of claims 1 to 6, wherein the thickness of the partition wall of the third resistance region is smaller than the thickness of the partition walls of the first resistance region and the second resistance region. An electrically heated carrier according to any one of claims 1 to 7, wherein a slit is formed by removing a portion of the partition wall of the third resistance region. a conductive honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall to define a plurality of cells that form flow paths from one end face to the other end face;
a first electrode layer provided in a strip shape on the surface of the outer peripheral wall in the extending direction of the cell; and
a second electrode layer provided in a strip shape on the surface of the outer peripheral wall in the extending direction of the cells, the second electrode layer being provided so as to face the first electrode layer across the central axis of the honeycomb structure section;
Equipped with
an electrically heated carrier, in a cross section perpendicular to the extension direction of the cell, in a region sandwiched between a pair of opposing outer wall portions on whose surfaces neither the first electrode layer nor the second electrode layer is provided, wherein a portion of the partition wall is missing, and the electrically heated carrier has one or more slits extending in a direction intersecting an imaginary line parallel to a straight line connecting the circumferential center of the first electrode layer and the circumferential center of the second electrode layer. An electrically heated carrier according to any one of claims 1 to 9;
and a cylindrical metal tube that houses the electrically heated carrier.