WO2021181743A1 - Electrically heated carrier and exhaust gas purification device - Google Patents

Abstract

An electrically heated carrier 1 according to the present invention is provided with: a columnar honeycomb structure 2 that generates heat when current is passed therethrough and that comprises an outer circumferential wall 20 and a division wall 21 which is disposed on the inner side of the outer circumferential wall 20 and which compartmentalizes and forms a plurality of cells 21a penetrating from one end face up to the other end face so as to form flow channels; and a pair of electrodes 3a, 3b disposed on an outer surface of the outer circumferential wall 20. The honeycomb structure 2 is composed of ceramics containing Si. The pair of electrodes 3a, 3b contain an electrically conductive material. Intermediate layers 4a, 4b are provided between the honeycomb structure 2 and the respective electrodes 3a, 3b. The intermediate layers have a porosity of 0-50%.

Description

Electric heating type carrier and exhaust gas purification device

The present invention relates to an electrically heated carrier and an exhaust gas purifying device.

As the ceramic carrier used for the electric heating catalyst (EHC), in Patent Document 1 below, a carrier having PTC characteristics is used, and more specifically, a matrix composed of a borosilicate containing an alkaline atom is used. Is disclosed. The PTC characteristic is a characteristic in which the electrical resistance increases as the temperature rises. By using a carrier having PTC characteristics, it is possible to improve the uneven temperature distribution caused by local heat generation due to the concentrated flow of current during energization heating.

The EHC is provided with an electrode, a base material, and a joint portion for joining the electrode and the base material. Since the joint is easily exposed to high-temperature exhaust gas, it is likely to be oxidized and lead to a local increase in electrical resistance. Patent Document 2 below discloses that the joint between the electrode and the base material contains a borosilicate containing an alkaline atom. By using a borosilicate containing an alkaline atom at the joint, oxidation of the metal at the joint is suppressed, and a local increase in electrical resistance at the joint is suppressed.

Japanese Unexamined Patent Publication No. 2019-012682 International Publication No. 2019/065381

As a result of the studies by the present inventors, when an electrode (specifically, an electrode containing a conductive material) and a honeycomb structure as a carrier containing silicon are combined, they are exposed to exhaust gas during firing or at a high temperature. At that time, it was found that the electrodes and / or the honeycomb structure may be brittle or deteriorated and damaged.

The present invention has been made to solve the above problems, and one of the purposes thereof is to reduce the possibility of embrittlement or deterioration of the honeycomb structure and electrodes even when heated to a high temperature. Provided are an electrically heated carrier and an exhaust gas purifying device.

One aspect of the electrically heated carrier according to the present invention is a partition wall that is disposed inside the outer peripheral wall and partitions a plurality of cells that penetrate from one end face to the other end face to form a flow path. A columnar honeycomb structure that generates heat when energized, and a pair of electrodes provided on the surface of the outer peripheral wall, and the honeycomb structure is made of Si-containing ceramics and has a pair. The electrode contains a conductive material, has an intermediate layer between the honeycomb structure and the electrode, and the porosity of the intermediate layer is 0 to 50%.

One aspect of the exhaust gas purification device according to the present invention includes the above-mentioned electric heating type carrier and a can body holding the electric heating type carrier.

According to the present invention, it is possible to provide an electrically heated carrier that can reduce the risk of embrittlement or deterioration of the honeycomb structure and electrodes even when heated to a high temperature.

It is a perspective view which shows the electric heating type carrier 1 in embodiment of this invention. It is sectional drawing which shows the electric heating type carrier 1 of FIG. FIG. 3 is an enlarged cross-sectional view showing an enlarged region III of FIG. It is explanatory drawing which shows the exhaust gas purification apparatus which concerns on embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The present invention is not limited to each embodiment, and the components can be modified and embodied without departing from the gist thereof. In addition, various inventions can be formed by appropriately combining the plurality of components disclosed in each embodiment. For example, some components may be removed from all the components shown in the embodiments. Furthermore, the components of different embodiments may be combined as appropriate.

<Electric heating type carrier>
FIG. 1 is a perspective view showing an electrically heated carrier 1 according to an embodiment of the present invention, FIG. 2 is a cross-sectional view orthogonal to the extending direction of the cell of the electrically heated carrier 1 of FIG. 1, and FIG. 3 is a view. It is an enlarged cross-sectional view which shows the region III of 2 in an enlarged manner.

As shown in FIGS. 1 to 3, the electrically heated carrier 1 of the present embodiment has a honeycomb structure 2, a pair of electrodes 3a and 3b, and a pair of intermediate layers 4a and 4b. According to the present invention, by providing the pair of intermediate layers 4a and 4b, it is possible to reduce the possibility that the honeycomb structure 2 and the electrodes 3a and 3b are embrittled or deteriorated even when heated to a high temperature. The present inventors speculate that the reason for this is as follows. The reason why the electrodes 3a and 3b and / or the honeycomb structure 2 are likely to be embrittled or deteriorated is that the silicon in the honeycomb structure 2 is an element that is relatively easy to move, and when the honeycomb structure 2 is heated to a high temperature. It is thought that this is because many elemental movements occur. Then, it is considered that the movement of silicon in the honeycomb structure 2 causes a change in the components of the honeycomb structure 2 and the electrodes 3a and 3b, which leads to embrittlement or deterioration of the honeycomb structure 2 and the electrodes 3a and 3b. ing. In the present invention, as described above, by providing the intermediate layers 4a and 4b between the honeycomb structure 2 and the electrodes 3a and 3b, such movement of silicon is suppressed, whereby the honeycomb structure 2 and the electrodes 3a are suppressed. , 3b is considered to reduce the risk of embrittlement or deterioration.

(1. Honeycomb structure)
The honeycomb structure 2 is a columnar structure, and partitions the outer peripheral wall 20 and a plurality of cells 21a arranged inside the outer peripheral wall 20 and penetrating from one end face to the other end face to form a flow path. It has a partition wall 21 to be formed.

The honeycomb structure 2 is made of a ceramic containing silicon, and as the ceramic, borosilicate containing SiC or an alkaline atom can be used. Examples of the alkaline atom include Na, Mg, K, Ca, Li, Be, Sr, Cs and Ba. The borosilicate may contain one or more kinds of alkali metal atoms, may contain one or more kinds of alkaline earth metal atoms, or may contain a combination thereof. The alkaline atom is more preferably Na, Mg, K, or Ca.

Although details will be described later, the honeycomb structure 2 may have a matrix composed of the above-mentioned borosilicate containing an alkaline atom and a domain composed of a conductive filler. The matrix is a portion that serves as a base material for the honeycomb structure 2. The matrix may be amorphous or crystalline. According to such a configuration, the region that controls the electric resistance when the EHC is energized and heated becomes the matrix that is the base material. The matrix has a smaller temperature dependence of electrical resistivity than the SiC material, and the electrical resistivity exhibits PTC characteristics (characteristics in which the electrical resistance increases as the temperature rises).

In the borosilicate, the total content of alkaline atoms may be 10% by mass or less. More preferably, it may be 5% by mass or less, or 2% by mass or less. According to such a configuration, it becomes easy to reduce the electric resistance of the matrix, and the electrical resistivity of the matrix shows more PTC characteristics. Further, it is possible to suppress the formation of an insulating glass film due to the segregation of alkaline atoms on the surface side of the honeycomb structure 2 during firing in an oxidizing atmosphere. The lower limit is not particularly limited, but the total content of alkaline atoms may be 0.01% by mass or more, or 0.2% by mass or more. Alkaline atoms may be intentionally added to suppress the oxidation of the conductive filler. Further, since it is an element that is relatively easily mixed from the raw material of the honeycomb structure 2, it complicates the manufacturing process to completely remove it, and therefore, it is usually included within the above range. In the honeycomb structure 2, it is possible to reduce alkaline atoms by using boric acid instead of using borosilicate glass containing alkaline atoms as a raw material. Here, the "total content of alkaline atoms" indicates, when the borosilicate contains one kind of alkaline atoms, the mass% of the one kind of alkaline atoms. When the borosilicate contains a plurality of alkaline atoms, the total content (mass%) with the content (mass%) of each of the plurality of alkaline atoms is shown.

The content of each of the B (boron) atom, Si (silicon) atom, and O (oxygen) atom constituting the borosilicate is preferably in the following range, for example. The content of B atom in borosilicate is 0.1% by mass or more and 5% by mass or less.

The content of Si atom in borosilicate is 5% by mass or more and 40% by mass or less.

The content of O atom in borosilicate is 40% by mass or more and 85% by mass or less. According to such a configuration, it is possible to easily show the PTC characteristics in the honeycomb structure 2.

As the borosilicate, for example, aluminoborosilicate can be used. According to such a configuration, it is possible to obtain a honeycomb structure 2 in which the temperature dependence of the electrical resistivity is small, the electrical resistivity exhibits PTC characteristics, or the temperature dependence of the electrical resistivity is suppressed. can. The content of Al atom in the aluminum borosilicate may be, for example, 0.5% by mass or more and 10% by mass or less.

Examples of the atoms contained in the borosilicate constituting the matrix in addition to the atoms in the above-mentioned borosilicate include Fe and C. Of the above-mentioned atoms, the contents of alkaline atoms, Si, O, and Al can be measured using an electron probe microanalyzer (EPMA) analyzer. Of the above-mentioned atoms, the B content can be measured using an inductively coupled plasma (ICP) analyzer. According to the ICP analysis, the B content in the entire honeycomb structure 2 is measured, so that the obtained measurement result is converted into the B content in the borosilicate.

The honeycomb structure 2 may have only a matrix, or may have one or more other substances in addition to the matrix. Examples of other substances include fillers, materials that reduce the coefficient of thermal expansion, materials that increase thermal conductivity, materials that improve strength, and the like.

When the honeycomb structure 2 has a matrix and a conductive filler, the electrical resistivity of the entire honeycomb structure 2 is determined by adding the electrical resistivity of the matrix and the electrical resistivity of the conductive filler. .. Therefore, the electrical resistivity of the honeycomb structure 2 can be controlled by adjusting the conductivity of the conductive filler and the content of the conductive filler. The electrical resistivity of the conductive filler may exhibit either PTC characteristics (characteristics in which the electric resistance increases as the temperature rises) or NTC characteristics (characteristics in which the electric resistance decreases as the temperature rises), and electricity. The resistivity does not have to be temperature dependent.

The conductive filler may contain Si atoms. According to such a configuration, it is possible to improve the shape stability of the honeycomb structure 2.

Examples of the conductive filler containing Si atoms include Si particles, Fe—Si particles, SiW particles, SiC particles, Si—Mo particles, Si—Ti particles and the like. These can be used alone or in combination of two or more.

The Si particles may be Si particles doped with a dopant. Dopants include boron (B), aluminum (Al), gallium (Ga), indium (In), nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) and the like. Can be mentioned. The dopant concentration may be contained as a dopant in the silicon particles in the range of ^{1 × 10 16} to 5 × 10 ²⁰ pieces / cm ^3. Here, in general, the volume resistivity of the honeycomb structure 2 decreases as the concentration of the dopant in the Si particles increases, and the volume resistivity of the honeycomb structure 2 increases as the concentration of the dopant in the Si particles decreases.

The amount of dopant in the silicon particles contained in the honeycomb structure 2 ^{is preferably 5 × 10 16} to 5 × 10 ²⁰ pieces / cm ³ , and 5 × 10 ¹⁷ to 5 × 10 ²⁰ pieces / cm ^3. More preferred. If the dopant in the Si particles contained in the honeycomb structure 2 is a homologous element, it may contain a plurality of types of elements because it can exhibit conductivity without being affected by counterdoping. Further, it is more preferable that the dopant is one or two selected from the group consisting of B and Al. It is also preferable that it is one or two selected from the group consisting of N and P.

When the honeycomb structure 2 has a matrix and a conductive filler, the honeycomb structure 2 may have a configuration in which the matrix and the conductive filler are contained in a total of 50 vol% or more.

The honeycomb structure 2 contains Si, and this Si may be derived by containing a Si atom in a borosilicate containing SiC or an alkaline atom, or a conductive filler containing a Si atom as a conductive filler. It may be derived from this using a filler.

The rate of increase in electrical resistance of the honeycomb structure 2 ^{is preferably 1 × 10 -8} to 5 × 10 ^-4 Ω · m / K. When the rate of increase in electrical resistance of the honeycomb structure 2 is 1 × 10 ^-8 Ω · m / K or more, it becomes easy to suppress the temperature distribution during energization and heating. When the rate of increase in electrical resistance of the honeycomb structure 2 is 5 × 10 ^-4 Ω · m / K or less, the change in resistance during energization and heating can be reduced. The rate of increase in electrical resistance of the honeycomb structure 2 ^{is more preferably 5 × 10 -8} to 1 × 10 ^-4 Ω ・ m / K, and 1 × 10 ^-7 to 1 × 10 ^-4 Ω ・ m / K. It is even more preferable to have it. For the electrical resistivity increase rate of the honeycomb structure 2, first, the electrical resistivity at two points at 50 ° C. and 400 ° C. is measured by the four-terminal method, and the electrical resistivity at 50 ° C. is subtracted from the electrical resistivity at 400 ° C. It can be obtained by dividing the value derived in this manner by the temperature difference of 350 ° C. between 400 ° C. and 50 ° C. to calculate the rate of increase in electrical resistance.

The outer shape of the honeycomb structure 2 is not particularly limited as long as it is columnar. It can have a columnar shape (octagonal shape, etc.). ^{Further, the size of the honeycomb structure 2 is preferably 2000 to 20000 mm 2} and preferably 5000 to 17000 mm for the reason of improving heat resistance (suppressing cracks entering the peripheral wall 20 in the circumferential direction). ² is more preferable.

The honeycomb structure 2 has conductivity. The honeycomb structure 2 is not particularly limited in electrical resistivity as long as it can be energized and generated by Joule heat ^{, but it is preferably 1 × 10 -5} to 2Ω · m, and 5 × 10 ^-5 to It is more preferably 1 Ω · m, and even more preferably 1 × 10 ^-4 to 0.5 Ω · m. In the present invention, the electrical resistivity of the honeycomb structure 2 is a value measured at 25 ° C. by the four-terminal method.

There is no limitation on the shape of the cell in the cross section perpendicular to the extending direction of the cell 21a, but it is preferably a quadrangle, a hexagon, an octagon, or a combination thereof. Among these, a quadrangle and a hexagon are preferable. By making the cell shape in this way, the pressure loss when the exhaust gas is passed through the honeycomb structure 2 is reduced, and the purification performance of the catalyst is excellent. A quadrangle is particularly preferable from the viewpoint of easily achieving both structural strength and heating uniformity.

The thickness of the partition wall 21 forming the cell 21a is preferably 0.1 to 0.3 mm, more preferably 0.1 to 0.2 mm. When the thickness of the partition wall 21 is 0.1 mm or more, it is possible to suppress a decrease in the strength of the honeycomb structure 2. When the thickness of the partition wall 21 is 0.3 mm or less, it is possible to suppress an increase in pressure loss when exhaust gas is flowed when the honeycomb structure 2 is used as a catalyst carrier and a catalyst is supported. In the present invention, the thickness of the partition wall 21 is defined as the length of a portion of a line segment connecting the centers of gravity of adjacent cells 21a that passes through the partition wall 21 in a cross section perpendicular to the extending direction of the cell 21a.

^{The honeycomb structure 2 preferably has a cell density of 40 to 150 cells / cm 2} , and more preferably 60 to 100 cells / cm ² in a cross section perpendicular to the flow path direction of the cells 21a. By setting the cell density in such a range, the purification performance of the catalyst can be improved while the pressure loss when the exhaust gas is passed is reduced. When the cell density is 40 cells / cm ² or more, a sufficient catalyst-supporting area is secured. When the cell density is 150 cells / cm ² or less, when the honeycomb structure 2 is used as a catalyst carrier and the catalyst is supported, it is possible to prevent the pressure loss when the exhaust gas is flowed from becoming too large. The cell density is a value obtained by dividing the number of cells by the area of one bottom surface portion of the honeycomb structure 2 excluding the outer peripheral wall 20 portion.

Providing the outer peripheral wall 20 of the honeycomb structure 2 is useful from the viewpoint of ensuring the structural strength of the honeycomb structure 2 and suppressing the fluid flowing through the cell 21a from leaking from the outer peripheral wall 20. Specifically, the thickness of the outer peripheral wall 20 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 20 is made too thick, the strength becomes too high, the strength balance with the partition wall 21 is lost, and the heat impact resistance is lowered. Therefore, the thickness of the outer peripheral wall 20 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 20 is the normal direction with respect to the tangent line of the outer peripheral wall 20 at the measurement location when the portion of the outer peripheral wall 20 whose thickness is to be measured is observed in a cross section perpendicular to the extending direction of the cell. Defined as thickness.

The partition wall 21 preferably has a porosity of less than 30%. If the porosity of the partition wall 21 is less than 30%, the risk of damage during canning is reduced. The porosity of the partition wall 21 is more preferably 20% or less, and even more preferably 10% or less. When the honeycomb structure 2 is used as a catalyst carrier, the partition wall 21 has a porosity of 1% or more in order to suppress peeling between the partition wall 21 and the catalyst when the catalyst is supported on the partition wall 21. It is preferably 2% or more, and even more preferably 5% or more. The porosity is a value calculated by binarizing the pores and the non-pores (specifically, the ceramic material portion) in the SEM observation image of the partition wall 21.

(2. Electrode)
The honeycomb structure 2 is provided with a pair of electrodes 3a and 3b on the surface of the outer peripheral wall 20, and the electrodes 3a and 3b contain a conductive material. The electrodes 3a and 3b are arranged so as to face each other with the central axis of the honeycomb structure 2 interposed therebetween. However, the positions of the electrodes 3a and 3b in the circumferential direction of the honeycomb structure 2 are arbitrary.

The electrodes 3a and 3b of the present embodiment have electrode layers 30a and 30b and electrode terminals 31a and 31b, respectively. The electrode layers 30a and 30b have a strip-shaped outer shape extending in the circumferential direction of the outer peripheral wall 20 and the extending direction of the cell, and are interposed between the intermediate layers 4a and 4b and the electrode terminals 31a and 31b, which will be described later. Has been done. The electrode terminals 31a and 31b have a columnar outer shape, and are provided so as to stand up from the surfaces of the electrode layers 30a and 30b.

The electrode terminals 31a and 31b are electrically bonded to the electrode layers 30a and 30b, and when a voltage is applied to the electrode terminals 31a and 31b, the honeycomb structure 2 can be heated by Joule heat. Therefore, the honeycomb structure 2 can be suitably used as a heater. The applied voltage is preferably 12 to 900 V, more preferably 48 to 600 V, but the applied voltage can be changed as appropriate.

The electrode layers 30a and 30b may be omitted. When the electrode layers 30a and 30b are omitted, the electrode terminals 31a and 31b are provided so as to stand up against the intermediate layers 4a and 4b.

There are no particular restrictions on the formation regions of the electrode layers 30a and 30b, but each of the electrode layers 30a and 30b has a length of 80% or more between both bottom surfaces of the honeycomb structure 2, preferably 90% or more. Therefore, it is more preferable that the current extends over the entire length from the viewpoint that the current easily spreads in the axial direction of the electrode layers 30a and 30b. By facilitating the spread of the electric current, the uniform heat generation property of the honeycomb structure 2 can be enhanced.

The thickness of each of the electrode layers 30a and 30b is preferably 0.01 to 5 mm, more preferably 0.01 to 3 mm. By setting it in such a range, uniform heat generation can be enhanced. When the thickness of each of the electrode layers 30a and 30b is 0.01 mm or more, the electric resistance is appropriately controlled and heat can be generated more uniformly. If it is 5 mm or less, the risk of damage during canning is reduced. The thickness of each of the electrode layers 30a and 30b is such that when the portion of the electrode layer 30a and 30b whose thickness is to be measured is observed in a cross section perpendicular to the stretching direction of the cell, the measurement portion on the outer surface of each of the electrode layers 30a and 30b. Is defined as the thickness in the normal direction with respect to the tangent line in.

The electrical resistivity of the electrode layers 30a and 30b is not particularly limited, but is preferably 1 × 10 ^-5 to 5 × 10 ^-1 Ω · m. When the electrical resistance of the electrode layers 30a and 30b is 5 × 10 ^-1 Ω · m or less, the resistance at the time of energization heating can be reduced. The electrical resistance of the electrode layers 30a and 30b ^{is more preferably 1 × 10 -4} to 2 × 10 ^-1 Ω · m, and further preferably 5 × 10 ^-3 to 1 × 10 ^-1 Ω · m. More preferred. In the present invention, the electrical resistivity of the electrode layers 30a and 30b is a value measured at 25 ° C. by the four-terminal method.

The sizes of the electrode terminals 31a and 31b are not limited, but for example, ^{they are formed in a columnar shape having an area of both end faces of 10 to 800 mm 2} and a length of 10 to 100 mm in the direction in which the electrode terminals 31a and 31b stand up. can do. The cross-sectional area of the electrode terminals 31a and 31b on the plane orthogonal to the length direction L of the electrode terminals 31a and 31b may be uniform in the length direction L of the electrode terminals 31a and 31b, but in the length direction L. It may change. The cross-sectional area of the ends (bases) of the electrode terminals 31a and 31b on the honeycomb structure 2 side may be wider than the cross-sectional area on the tip side of the electrode terminals 31a and 31b. Further, in the electrode terminals 31a and 31b, at least at the base of the electrode terminals 31a and 31b, the cross-sectional area of the electrode terminals 31a and 31b becomes the bottom area of the electrode terminals 31a and 31b (on the honeycomb structure 2 side) as the distance from the honeycomb structure 2 increases. It may have a shape that gradually (continuously or stepwise) decreases from the end face (bottom surface) area). For example, the bases of the electrode terminals 31a and 31b may have a truncated cone shape. The areas of both end faces of the electrode terminals 31a and 31b may be different from each other.

The materials of the electrode layers 30a and 30b and the electrode terminals 31a and 31b are formed of a conductive material. Examples of the conductive material include oxide ceramics, metals or mixtures of metal compounds and oxide ceramics, carbon, oxide ceramics containing carbon, and composite materials containing carbon. The materials of the electrode layers 30a and 30b and the electrode terminals 31a and 31b may be the same.

The metal may be a single metal or an alloy, and for example, silicon, aluminum, iron, stainless steel, titanium, tungsten, Ni—Cr alloy, zinc, copper, nickel, silver, gold and the like can be preferably used. Examples of metal compounds include those other than oxide ceramics, such as metal oxides, metal nitrides, metal carbides, metal siliceates, metal borides, and composite oxides, such as FeSi ₂ , CrSi ₂ , and alumina. Titanium oxide, tin oxide (Sb-doped), indium oxide (Sn-doped), zinc oxide (Al-doped) and the like can be preferably used. Both the metal and the metal compound may be one kind alone, or two or more kinds may be used in combination. Specific examples of oxide ceramics include glass, cordierite, and mullite. The glass may further contain an oxide consisting of at least one component selected from the group consisting of B, Mg, Al, Si, P, Ti and Zr.

As the carbon, it is preferable that the main component is carbon such as graphite (graphite), carbon black, carbon fiber (carbon fiber), charcoal / activated charcoal, coke, fullerene, and carbon nanotubes. The fact that carbon is the main component means that the carbon content is 50% by mass or more with respect to all the components constituting the electrode terminals 31a and 31b. The carbon content is more preferably 80% by mass or more, and even more preferably 90% by mass or more.

Of these materials, when the electrodes 3a and 3b are formed of carbon or a metal such as nickel or aluminum, they have the property of easily binding to Si atoms and form Si and VDD of the honeycomb structure 2. Therefore, by providing the intermediate layers 4a and 4b of the present invention, the embrittlement or deterioration suppressing effect on the honeycomb structure 2 and the electrodes 3a and 3b can be more effectively obtained.

Metal terminals may be joined to the tips of the electrode terminals 31a and 31b, respectively. The carbon electrode terminals 31a and 31b can be joined to the metal terminal by caulking, welding, brazing, a conductive adhesive or the like. As the material of the metal terminal, a conductive metal such as an iron alloy or a nickel alloy can be adopted.

(3. Middle layer)
Intermediate layers 4a and 4b are provided between the honeycomb structure 2 and the electrodes 3a and 3b. The intermediate layers 4a and 4b of the present embodiment are interposed between the outer peripheral wall 20 of the honeycomb structure 2 and the electrode layers 30a and 30b of the electrodes 3a and 3b. The intermediate layers 4a and 4b inhibit the silicon contained in the outer peripheral wall 20 from moving to the electrode layers 30a and 30b. In other words, by providing the intermediate layers 4a and 4b between the honeycomb structure 2 and the electrodes 3a and 3b, the honeycomb structure 2 and the electrodes 3a and 3b are in full and direct contact with each other. Compared with the case, the movement of silicon is suppressed. Although it depends on the material of the electrodes 3a and 3b, for example, when a composite material of metal and ceramics containing nickel is used for the electrodes 3a and 3b, the intermediate layers 4a and 4b are provided, so that the electrodes 3a are provided. , It is possible to avoid direct contact between the nickel in 3b and the silicon in the honeycomb structure 2. Even if the temperature of the honeycomb structure 2 is 1000 ° C. or higher, nickel silicide, which is a brittle metal compound and suppresses the movement of silicon from the honeycomb structure 2 to the nickel side ( electrodes 3a, 3b side), Formation can be suppressed.

It is preferable that the extending region of the intermediate layers 4a and 4b is the same size as the extending region of the electrode layers 30a and 30b ( electrodes 3a and 3b) or is wider than the extending region thereof. In other words, it is preferable that there is no region where the electrode layers 30a and 30b are in direct contact with the outer peripheral wall 20. This is to suppress the movement of silicon more reliably. However, it is not excluded that the intermediate layers 4a and 4b are partially provided between the electrode layers 30a and 30b and the outer peripheral wall 20. Even in the embodiment in which the intermediate layers 4a and 4b are partially provided, the movement of silicon can be suppressed as compared with the case where the honeycomb structure 2 and the electrodes 3a and 3b are in full and direct contact with each other. ..

Although it depends on the material of the honeycomb structure 2 and the electrodes 3a and 3b, the intermediate layers 4a and 4b are appropriately designed so as to relieve the stress generated between the honeycomb structure 2 and the electrodes 3a and 3b. Is also one of the preferred forms. For example, the stress generated when the electrodes 3a and 3b are installed by brazing and / or firing, the stress generated due to the difference in the thermal expansion coefficient between the honeycomb structure 2 and the electrodes 3a and 3b, and the temperature generated during use. The intermediate layers 4a and 4b can also play a role of relieving the stress caused by the difference in distribution.

As shown in FIG. 3, the outer surface (diameter outer surface) of the intermediate layers 4a and 4b can form the same curved surface as the outer surface (diameter outer surface) of the outer peripheral wall 20. It is preferable that no step or groove is formed at the boundary between the intermediate layers 4a and 4b and the outer peripheral wall 20. The intermediate layers 4a and 4b can be formed by altering a part of the outer peripheral wall 20. A part of the outer peripheral wall 20 is scraped off to form a groove, and a member having the same shape as the groove is fitted into the groove, or the materials of the intermediate layers 4a and 4b are applied or piled up in the groove to form the intermediate layer 4a, 4b may be formed. The intermediate layers 4a and 4b may form a convex portion that protrudes outward in the radial direction from the outer peripheral surface of the outer peripheral wall 20.

Although not shown, the outer surface (diameter inner surface) of the intermediate layers 4a and 4b may form the same curved surface as the outer surface (diameter inner surface) of the electrode layers 30a and 30b ( electrodes 3a and 3b). In this case, it is preferable that no step or groove is formed at the boundary between the intermediate layers 4a and 4b and the electrode layers 30a and 30b. The intermediate layers 4a and 4b can be formed by altering a part of the electrode layers 30a and 30b. A part of the electrode layers 30a and 30b is scraped off to form a groove, and a member having the same shape as the groove is fitted into the groove, or the material of the intermediate layers 4a and 4b is applied or piled up in the groove to form an intermediate layer. 4a and 4b may be formed. The intermediate layers 4a and 4b may form a convex portion that protrudes inward in the radial direction from the outer peripheral surface of the electrode layers 30a and 30b.

The thickness of the intermediate layers 4a and 4b is preferably 0.03 to 2 mm, more preferably 0.05 to 1 mm, and even more preferably 0.1 to 0.5 mm. By setting the thickness of the intermediate layers 4a and 4b to 0.03 mm or more, the electrodes 3a and 3b can be kept at a relatively low temperature even when the honeycomb structure 2 becomes hot due to automobile exhaust gas or the like. By reducing the thickness of the intermediate layers 4a and 4b to 2 mm or less, the structural influence on the honeycomb structure 2, the electrode layers 30a and 30b or the electrically heated carrier 1 can be reduced.

The intermediate layers 4a and 4b can have pores. Young's modulus can be controlled by having pores in the intermediate layers 4a and 4b. The porosity of the intermediate layers 4a and 4b is preferably 0 to 50%, more preferably 0 to 30%. From the viewpoint of the strength between the honeycomb structure 2 and the electrode layers 30a and 30b, the porosity of the intermediate layers 4a and 4b is preferably 50% or less.

The thermal conductivity of the intermediate layers 4a and 4b is preferably 1 W / mk or more, and more preferably 5 W / mk or more. When the thermal conductivity is 1 W / mk or more, the heat of the honeycomb structure 2 can be quickly transferred to the outside without being retained at the interface with the electrodes 3a and 3b, so that the honeycomb structure 2 and the electrodes 3a can be quickly transferred to the outside. , 3b can suppress brittleness or deterioration.

Preferably the intermediate layer 4a, the thermal expansion coefficient of the 4b alpha is 10 × 10 ^-6 or less, more preferably 6 × 10 ^-6 or less. With this configuration, the thermal stress between the honeycomb structure-intermediate layer-electrode layer can be relaxed.

The Young's modulus of the intermediate layers 4a and 4b is preferably 10 to 100 GPa. When the Young's modulus is 10 to 100 GPa, the stress between the honeycomb structure-intermediate layer-electrode layer can be relaxed.

As the material of the intermediate layers 4a and 4b, a diffusion inhibitor containing at least one element selected from the group consisting of zirconium, titanium, tantalum, niobium, vanadium, tungsten, molybdenum, chromium, silicon and manganese is mixed. Is preferable. By containing the above elements, the movement of silicon can be suppressed, and the embrittlement or deterioration of the honeycomb structure 2 and the electrodes 3a and 3b can be suppressed.

When selecting the materials of the intermediate layers 4a and 4b, it is conceivable to take into consideration other characteristics such as thermal conductivity, coefficient of thermal expansion and Young's modulus in addition to the above-mentioned diffusion prevention. In addition to preventing diffusion, the material of the intermediate layers 4a, 4b is at least selected from the group consisting of tungsten, molybdenum, titanium, niobium and vanadium in order to facilitate the acquisition of other properties desired as the intermediate layers 4a, 4b. A material containing one element is more preferable, and a material containing at least one element selected from the group consisting of tungsten, titanium and niobium is further preferable. Twice

<Catalyst>
By supporting the catalyst on the electroheating carrier 1, the electroheating carrier 1 can be used as the catalyst carrier. For example, a fluid such as automobile exhaust gas can flow through the flow paths of the plurality of cells 21a. Examples of the catalyst include noble metal-based catalysts and catalysts other than these. As the noble metal catalyst, a noble metal such as platinum (Pt), palladium (Pd), or rhodium (Rh) is supported on the surface of the alumina pores, and a three-way catalyst containing a co-catalyst such as ceria or zirconia, an oxidation catalyst, or an alkali. An example is a NOx storage reduction catalyst (LNT catalyst) containing earth metal and platinum as storage components of nitrogen oxide (NOx). Examples of catalysts that do not use noble metals include NOx selective reduction catalysts (SCR catalysts) containing copper-substituted or iron-substituted zeolites. Further, two or more kinds of catalysts selected from the group consisting of these catalysts may be used. The method of supporting the catalyst is also not particularly limited, and can be carried out according to the conventional method of supporting the catalyst on the honeycomb structure 2.

<Manufacturing method of electrically heated carrier>
Next, a method for producing the electroheated carrier according to the present invention will be exemplified. In one embodiment, the method for producing an electrically heated carrier of the present invention includes a step A1 for obtaining an unfired honeycomb structure with an electrode terminal forming paste and a honeycomb structure with an electrode terminal forming paste by firing the unfired honeycomb structure. The step A2 for obtaining the structure is included. Further, as another embodiment, the electrode layer forming paste and the electrode terminal forming paste may be attached to the honeycomb structure after calcination. Further, for the electrode terminals made of carbon, the electrode terminals made of carbon may be attached to the honeycomb structure.

In step A1, a columnar honeycomb molded body that is a precursor of the honeycomb structure is produced, and an electrode layer forming paste is applied to the side surface of the honeycomb molded body to obtain an unfired honeycomb structure with the electrode layer forming paste. This is a step of providing an electrode terminal forming paste on the electrode layer forming paste to obtain an unfired honeycomb structure with the electrode terminal forming paste.

To prepare the honeycomb molded product, first, boric acid, a conductive filler containing Si atoms, and kaolin are mixed. Alternatively, a borosilicate containing an alkaline atom, a conductive filler containing a Si atom, and kaolin are mixed. The borosilicate may have a fibrous or particulate shape, and is preferably fibrous because it improves the extrudability of the mixture. In the mixture, the mass ratio of boric acid is preferably 4 or more and 8 or less in order to facilitate obtaining the honeycomb structure 2 having a small temperature dependence of electrical resistivity. The content of boron contained in the borosilicate can be increased by increasing the firing temperature described later. As the amount of boron doped in the silicate is increased, the electrical resistance of the honeycomb structure 2 can be further reduced.

Next, add a binder and water to the mixture. Examples of the binder include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol and the like. The binder content can be, for example, about 2% by mass.

Next, after kneading the obtained molding raw materials to form a clay, the clay is extruded to produce a honeycomb molded body. In extrusion molding, a mouthpiece having a desired overall shape, cell shape, partition wall thickness, cell density and the like can be used. Next, it is preferable to dry the obtained honeycomb molded product. When the length in the central axis direction of the honeycomb molded body is not the desired length, both bottom portions of the honeycomb molded body can be cut to obtain the desired length. The dried honeycomb molded body is called a columnar honeycomb dried body.

Next, prepare an intermediate layer forming paste for forming the intermediate layer. The intermediate layer forming paste can be prepared, for example, by mixing an anti-diffusion material containing the above elements, optionally a binder and water.

Next, the obtained intermediate layer forming paste is applied to the side surface of the honeycomb molded body (typically, the columnar honeycomb dried body) to obtain an unfired honeycomb structure with the intermediate layer forming paste. The method of applying the intermediate layer forming paste to the honeycomb molded body can be performed according to a known method for producing a honeycomb structure.

Next, the electrode layer forming paste for forming the electrode layer is prepared. The electrode layer forming paste can be produced by mixing a conductive material blended according to the required characteristics of the electrode layer with a binder and water.

Next, the obtained electrode layer forming paste is applied to the side surface of the honeycomb molded body with the intermediate layer forming paste to obtain an unfired honeycomb structure with the electrode layer forming paste. The method of applying the electrode layer forming paste to the honeycomb molded body can be performed according to a known method for producing a honeycomb structure.

As an example of changing the method for manufacturing the honeycomb structure, the honeycomb molded body may be fired once before applying the intermediate layer forming paste or the electrode layer forming paste in step A1. That is, in this modified example, the honeycomb molded body is fired to produce a columnar honeycomb fired body, and the intermediate layer forming paste or the electrode layer forming paste is applied to the columnar honeycomb molded body.

Next, the electrode terminal forming material for forming the electrode terminal is prepared. The electrode terminal forming material can be kneaded by appropriately adding various additives to the conductive material blended according to the required characteristics of the electrode terminals. Next, the prepared and kneaded electrode terminal forming material is formed into a predetermined shape by press molding, and dried and / or fired. Since the electrode terminals are deformed by shrinkage during drying and / or firing, it is preferable to perform cutting and / or polishing after drying and / or firing. Next, the electrode terminals are provided in a predetermined shape so as to stand up from the surface of the electrode layer on the honeycomb structure. As a method of providing the honeycomb structure so as to stand up from the surface of the electrode layer, an electrode layer forming paste can be used.

In step A2, the unfired honeycomb structure with the electrode terminal forming paste is fired to obtain the honeycomb structure with the electrode terminals. The firing conditions can be under an inert gas atmosphere or an atmospheric atmosphere, below atmospheric pressure, a firing temperature of 1150 to 1350 ° C., and a firing time of 0.1 to 50 hours. The firing atmosphere may be, for example, an inert gas atmosphere, and the firing pressure may be normal pressure. In order to reduce the electrical resistance of the honeycomb structure 2, it is preferable to reduce the residual oxygen from the viewpoint of preventing oxidation, and it is not possible after ^{the atmosphere at the time of firing is set to a high vacuum of 1.0 × 10 -4 Pa or more.} It is preferable to purge the active gas and fire it. Examples of the inert gas atmosphere include an N ₂ gas atmosphere, a helium gas atmosphere, and an argon gas atmosphere. The unfired honeycomb structure with the electrode terminal forming paste may be dried before firing. Further, before firing, degreasing may be performed in order to remove the binder and the like. In this way, an electrically heated carrier in which the electrode terminals are electrically connected to the electrode layer is obtained.

<Exhaust gas purification device>
Next, FIG. 4 is an explanatory diagram showing an exhaust gas purification device according to an embodiment of the present invention. The electrically heated carrier 1 according to the embodiment of the present invention described above can be used in an exhaust gas purification device. The exhaust gas purifying device includes an electrically heated carrier 1 and a metal can body 5 that holds the electrically heated carrier 1. As shown in FIG. 4, the metal electrodes 6a and 6b bonded to the electrode terminals 31a and 31b may be further provided. In the exhaust gas purification device, the electrically heated carrier 1 is installed in the middle of the exhaust gas flow path for flowing the exhaust gas from the engine.

1 Electric heating type carrier 2 Honeycomb structure 20 Peripheral wall 21 Partition wall 21a Cell 3a, 3b Electrode 30a, 30b Electrode layer 31a, 31b Electrode terminal 4a, 4b Intermediate layer

Claims (11)

1. It has an outer peripheral wall and a partition wall that is disposed inside the outer peripheral wall and forms a plurality of cells that penetrate from one end face to the other end face to form a flow path, and generates heat when energized. Columnar honeycomb structure and
   A pair of electrodes provided on the surface of the outer peripheral wall and
   With
   The honeycomb structure is made of ceramics containing Si,
   The pair of electrodes contains a conductive material and
   It has an intermediate layer between the honeycomb structure and the electrodes.
   The porosity of the intermediate layer is 0 to 50%.
   Electric heating type carrier.
2. The thermal conductivity of the intermediate layer is 1 W / mk or more.
   The electrically heated carrier according to claim 1.
3. The coefficient of thermal expansion α of the intermediate layer is 10 × 10 ^-6 or less.
   The electroheated carrier according to claim 1 or 2.
4. The Young's modulus of the intermediate layer is 10 to 100 GPa.
   The electrically heated carrier according to any one of claims 1 to 3.
5. The material of the intermediate layer contains at least one element selected from the group consisting of zirconium, titanium, tantalum, niobium, vanadium, tungsten, molybdenum, chromium, silicon and manganese.
   The electrically heated carrier according to any one of claims 1 to 4.
6. The electrode has a columnar electrode terminal.
   The electrically heated carrier according to any one of claims 1 to 5.
7. The electrode further has a band-shaped electrode layer interposed between the intermediate layer and the electrode terminal.
   The electrically heated carrier according to claim 6.
8. The electroheated carrier according to any one of claims 1 to 7, wherein the ceramic containing Si is a borosilicate containing SiC or an alkaline atom.
9. The electricity according to any one of claims 1 to 8, wherein the honeycomb structure has a matrix composed of a borosilicate containing an alkaline atom and a domain composed of a conductive filler. Heated carrier.
10. The porosity of the partition wall is less than 30%.
    The electrically heated carrier according to any one of claims 1 to 9.
11. The electrically heated carrier according to any one of claims 1 to 10.
    A can body that holds the electroheated carrier.
    Exhaust gas purification device.

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