JP7579646B2 - SiC powder and its manufacturing method, electrically heated honeycomb structure and its manufacturing method - Google Patents

Description

The present invention relates to SiC powder and a manufacturing method thereof. The present invention also relates to a honeycomb structure that can also function as a heater by applying a voltage and a manufacturing method thereof.

Conventionally, ceramic honeycomb structures have been used as base materials for electrically heated catalysts (EHCs) and ceramic heaters for purifying exhaust gas. In such applications, the honeycomb structure is heated by connecting metal terminals to a pair of electrodes on the honeycomb structure and applying a voltage. For example, an EHC is an exhaust purification device that is installed in the exhaust path of an automobile or the like and purifies the exhaust gas emitted from the engine. This EHC supports a catalyst, and by heating the EHC, the catalyst is heated to a temperature required for activation.

Conventionally, a technology that focuses on the electrical resistivity of the electrode part in order to improve the uniformity of the current flowing through the EHC is known. JP 2014-198320 A (Patent Document 1) proposes that the electrode part is made of a porous body in which particles made of silicon carbide as an aggregate are bound by a binder, and that the silicon carbide as the aggregate constituting the electrode part contains β-SiC with stacking faults of 2% or less, and that the binder constituting the electrode part contains silicon and metal silicide. Patent Document 1 describes that this configuration makes it possible to lower the electrical resistivity of the electrode part compared to the electrode part of a conventional honeycomb structure. It also describes that this allows the current supplied to one of the pair of electrode parts to be transmitted well throughout the entire electrode part, and that the current flows uniformly from the electrode part to the entire honeycomb structure.

Furthermore, paragraph 0047 of Patent Document 1 states, "The average particle diameter of the particles made of silicon carbide used as aggregate is preferably 10 to 70 μm, more preferably 10 to 50 μm, and particularly preferably 15 to 40 μm. If the average particle diameter of the particles made of silicon carbide contained in the electrode portion is less than 10 μm, the electrical resistivity of the electrode portion tends to be high. Furthermore, if the average particle diameter of the particles made of silicon carbide contained in the electrode portion is more than 70 μm, the strength of the electrode portion tends to be reduced."

JP 2014-198320 A

Patent Document 1 discloses the technical idea of lowering the electrical resistivity of the electrode parts in order to allow current to flow uniformly throughout the honeycomb structure. It also specifically proposes using β-SiC with stacking faults of 2% or less as the aggregate that constitutes the electrode parts, and controlling the average particle size of the aggregate particles to 10 to 70 μm, in order to lower the electrical resistivity of the electrode parts.

However, Patent Document 1 does not sufficiently consider the change in electrical resistivity over time, and there is a concern that even if a low electrical resistivity is obtained initially, the electrical resistivity may increase with continued long-term use. According to the results of the inventor's investigations, it has been found that the electrical resistivity of the β-SiC described in Patent Document 1 is prone to increase with long-term use, which may reduce the heating performance of the honeycomb structure. For this reason, it is desirable to provide an electrically heated honeycomb structure whose electrical resistivity is unlikely to increase even with long-term use.

In view of the above circumstances, in one embodiment, the present invention aims to provide a SiC powder whose electrical resistivity is less likely to increase over time, and a method for manufacturing the same. In another embodiment, the present invention aims to provide an electrically heated honeycomb structure manufactured using such SiC powder, and a method for manufacturing the same.

[1]
Contains 70% by mass or more of β-SiC,
A SiC powder having a volume-based cumulative particle size distribution D50 of 8 to 35 μm and a D10 of 5 μm or more as measured by a laser diffraction method.
[2]
The SiC powder according to [1], wherein the cumulative volume of particles having a particle size of 5 μm or less in a volume-based cumulative particle size distribution measured by a laser diffraction method is 7% or less.
[3]
The SiC powder according to [1] or [2], wherein D50 is 15 to 35 μm and D10 is 7 to 20 μm in a volume-based cumulative particle size distribution measured by a laser diffraction method.
[4]
The SiC powder according to any one of [1] to [3], wherein D90 in a volume-based cumulative particle size distribution measured by a laser diffraction method is 100 μm or less.
[5]
The SiC powder according to any one of [1] to [4], wherein the stacking faults of β-SiC contained in the powder are 5% or less.
[6]
The SiC powder according to any one of [1] to [5], wherein the stacking faults of β-SiC contained in the powder exceed 2%.
[7]
The SiC powder according to any one of [1] to [6], further containing one or both of metallic silicon and silicide.
[8]
The SiC powder according to any one of [1] to [7], containing one or more third elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co, P, Cr and Zr.
[9]
The SiC powder according to [8], wherein the total concentration of the third element in the powder is 6 mass% or less.
[10]
A step of forming a compact by molding a mixture containing a SiC raw material powder and a powder containing a third element;
sintering the compact at a temperature of 1800° C. or less in an inert atmosphere to obtain a sintered body containing β-SiC;
pulverizing the sintered body to obtain a pulverized sintered body;
A step of classifying the pulverized sintered body to obtain a powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in a cumulative particle size distribution on a volume basis measured by a laser diffraction method;
A method for producing a SiC powder comprising the steps of:
[11]
The method for producing a SiC powder according to [10], wherein the powder has a cumulative volume of particles with a particle size of 5 μm or less in a volume-based cumulative particle size distribution measured by a laser diffraction method of 7% or less.
[12]
The method for producing a SiC powder according to [10] or [11], wherein the powder has a D50 of 15 to 35 μm and a D10 of 7 to 20 μm in a volume-based cumulative particle size distribution measured by a laser diffraction method.
[13]
The method for producing a SiC powder according to any one of [10] to [12], wherein the powder has a D90 of 100 μm or less in a volume-based cumulative particle size distribution measured by a laser diffraction method.
[14]
The third element-containing powder contains one or more third elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co, P, Cr and Zr. [10] - [13] The method for producing a SiC powder according to any one of claims 1 to 13.
[15]
The method for producing a SiC powder according to any one of [10] to [14], wherein the porosity of the sintered body is 35 to 80%.
[16]
The method for producing a SiC powder according to any one of [10] to [15], wherein the average pore diameter of the sintered body is 5 to 300 μm.
[17]
a step of forming and drying the clay to obtain a columnar honeycomb formed body having an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall, extending from the first bottom surface to the second bottom surface, and defining a plurality of cells that serve as fluid flow paths;
an electrode portion forming step of applying an electrode portion forming paste to a first region and a second region of a side surface of the honeycomb molded body or a honeycomb fired body obtained by firing the honeycomb molded body, and drying and firing the applied electrode portion forming paste to form a pair of electrode portions;
One or both of the clay and the electrode part forming paste contain the SiC powder according to any one of [1] to [9];
A method for manufacturing an electrically heated honeycomb structure.
[18]
An electrically heated honeycomb structure obtained by the manufacturing method according to [17].
[19]
An electrically heated honeycomb structure comprising the SiC powder according to any one of [1] to [9].

According to one embodiment of the present invention, a SiC powder whose electrical resistivity does not increase over time and a method for producing the same are provided. By using this SiC powder as a raw material for an electrically heated honeycomb structure, it is possible to obtain an electrically heated honeycomb structure that is highly durable and whose electrical resistance does not increase even after long-term use.

1 is a perspective view showing a honeycomb structure according to an embodiment of the present invention; FIG. 4 is a schematic diagram illustrating a method for measuring electrical resistance.

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

(1. SiC Powder)
In one embodiment, the SiC powder according to the present invention is
Contains 70% by mass or more of β-SiC,
In the cumulative particle size distribution on a volume basis measured by a laser diffraction method, D50 is 8 to 35 μm, and D10 is 5 μm or more.

(1-1 Particle size distribution of SiC powder)
In one embodiment of the SiC powder according to the present invention, D50 is 8 to 35 μm and D10 is 5 μm or more in the cumulative particle size distribution based on volume measured by a laser diffraction method. Preferably, D50 is 15 to 35 μm and D10 is 7 to 20 μm. More preferably, D50 is 20 to 30 μm and D10 is 12 to 20 μm. D50 refers to the particle size at 50% cumulative volume in the cumulative particle size distribution measured above. D10 refers to the particle size at 10% cumulative volume in the cumulative particle size distribution measured above. By having D50 of SiC powder of 8 μm or more and D10 of 5 μm or more, oxidation of SiC is suppressed, the electrical resistivity of the SiC powder itself is less likely to increase over time, and the increase over time of the electrical resistivity of a sintered body produced using this as a raw material powder is suppressed. Furthermore, by making D10 20 μm or less and D50 35 μm or less, moldability can be ensured.

In one embodiment of the SiC powder according to the present invention, the cumulative volume of particles with a particle size of 5 μm or less in the cumulative particle size distribution on a volume basis measured by a laser diffraction method is 7% or less. In addition to D50 and D10, the small cumulative volume of particles with a particle size of 5 μm or less further suppresses oxidation of SiC, further improving the effect of making it difficult for the electrical resistivity of the SiC powder itself to increase over time, and further suppressing the increase over time in the electrical resistivity of a sintered body produced using this as a raw material powder. The cumulative volume of particles with a particle size of 5 μm or less is preferably 5% or less, more preferably 2% or less, and even more preferably 1% or less.

In one embodiment of the SiC powder according to the present invention, the D90 in the cumulative particle size distribution on a volume basis measured by a laser diffraction method is 100 μm or less. When the D90 of the SiC powder is 100 μm or less, the moldability of the SiC powder is improved. The D90 of the SiC powder is preferably 80 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. D90 refers to the particle size at 90% of the cumulative volume in the cumulative particle size distribution measured above.

(1-2 Composition of SiC powder)
In one embodiment, the SiC powder according to the present invention contains 70% by mass or more of β-SiC. By making the SiC powder a main component of β-SiC, the initial electrical resistivity of the SiC powder itself can be kept low, and the initial electrical resistivity of a sintered body produced using this as a raw material powder can be reduced. The SiC powder preferably contains 75% by mass or more of β-SiC, and more preferably contains 80% by mass or more of β-SiC. There is no upper limit to the content of β-SiC in the SiC powder, and it can be made substantially 100% by mass, but considering the addition of a third element (typically a metal element) to suppress stacking faults and the remaining unreacted raw materials, the concentration of β-SiC in the SiC powder is usually 90% by mass or less, and typically 85% by mass or less.

In one embodiment, the SiC powder according to the present invention may further contain one or both of metallic silicon and silicide (typically a metal silicide). Metallic silicon is not particularly necessary, but metallic silicon used as a raw material for the SiC powder may remain. Silicide may also be formed when a third element (typically a metal element) described below, which is added to suppress stacking faults in β-SiC, reacts with metallic silicon used as a raw material for the SiC powder.

In one embodiment, the SiC powder according to the present invention contains one or more third elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co, P, Cr and Zr. Among these, it is more preferable to contain one or more third elements selected from the group consisting of Ti, Cr, Co, Ni, Al and Cu. These third elements suppress stacking faults in β-SiC, thereby contributing to keeping the initial electrical resistivity of the SiC powder itself low, and can also contribute to keeping the initial electrical resistivity of the sintered body produced using this as raw material powder low. In addition to the above, the SiC powder is advantageous in that the additional coexistence of one or more elements selected from the group consisting of N, P, Al and B keeps the initial electrical resistivity of the sintered body low. In this case, the total mass of one or more elements selected from the group consisting of N, P, Al, and B is preferably 0.0001 to 1 mass%, and more preferably 0.001 to 1 mass%, relative to the mass of SiC.

To enhance the effect of suppressing stacking faults in β-SiC, the total concentration of the above third elements in the SiC powder is preferably 1 mass% or more, and more preferably 3 mass% or more. On the other hand, if the concentration of the above third elements in the SiC powder becomes too high, the thermal expansion coefficient of the sintered body produced using the SiC powder as the raw material powder may become large. Therefore, the total concentration of the above third elements in the SiC powder is preferably 15 mass% or less, more preferably 10 mass% or less, and even more preferably 6 mass% or less.

(1-3 Stacking faults)
In one embodiment of the SiC powder according to the present invention, the stacking faults of β-SiC contained in the powder can be 5% or less, 3% or less, or 2% or less. On the other hand, in one embodiment of the SiC powder according to the present invention, the stacking faults of β-SiC contained in the powder can be more than 2%, 3% or more, or 4% or more, for example, 3 to 5%. By controlling the particle size distribution of the SiC powder within the above-mentioned range, even if there are many stacking faults in β-SiC, there is almost no adverse effect on the effect of making the electrical resistivity of the SiC powder itself less likely to increase over time.

Here, we will explain stacking faults in β-SiC. First, stacking faults are a type of planar lattice defect (planar defect), and when we think of perfect crystals as being made up of periodic stacking of atomic planes, they refer to a disruption in the regularity (order) of this stacking. In this specification, stacking faults (%) in β-SiC refers to the value calculated by the following formula (1). Here, A in the following (1) is the value calculated by the following formula (2).

The "33.6° peak intensity" in formula (2) refers to the peak intensity at a scattering angle (2θ) of 33.6° in the X-ray diffraction spectrum by X-ray diffraction (XRD). The "41.4° peak intensity" refers to the peak intensity at a scattering angle (2θ) of 41.4° in the X-ray diffraction spectrum by X-ray diffraction (XRD). In the above X-ray diffraction, a graphite monochromator is used, and X-ray diffraction analysis is performed using CuKα rays with a wavelength of 1.54 Å. The tube voltage is 50 kV and the tube current is 300 mA. The scanning speed is 2θ=2°min ⁻¹ , and the receiving slit is 0.3 mm. In this way, the peak intensity at the scattering angle 2θ=33.6° and the peak intensity at the scattering angle 2θ=41.4° in the X-ray diffraction spectrum are measured, "A" is calculated by the above formula (2), and the stacking faults of β-SiC can be obtained according to the above formula (1). The measurement is performed by sampling the SiC powder multiple times (e.g., 5 times or more), and the average value is taken as the measured value. In addition, as references describing stacking faults of β-SiC, for example, the following references 1 and 2 can be mentioned. Reference 1: Journal of the Ceramic Society of Japan, 99[12], pp. 1179-1184, (1991). Reference 2: Journal of the Ceramic Society of Japan, 106[5], pp. 483-487, (1998).

(1-4 Crystallite size of β-SiC)
The crystallite size of β-SiC is preferably 900 Å or more, more preferably 900 to 500,000 Å, and particularly preferably 1,000 to 500,000 Å. The crystallite size of β-SiC refers to a value calculated by the following formula (3). The following formula (3) is the Scherrer formula. Usually, one crystal grain is composed of fine crystals that can be regarded as multiple single crystals, and these fine crystals are called crystallites. The size of these crystallites is the above-mentioned "crystallite size." If the crystallite size of β-SiC is 900 Å or more, it contributes to keeping the initial electrical resistivity of the SiC powder itself low, and the initial electrical resistivity of the sintered body produced using this as a raw material powder can be effectively reduced.

In formula (3), "t (Å)" indicates the crystallite size (Å). "λ" indicates the X-ray wavelength (1.54 Å). "B" indicates the half-width of the peak at a scattering angle (2θ) of 35.6°. "θ _B " is 1/2 the scattering angle (2θ), that is, θ _B = 17.8°. The X-ray diffraction spectrum by X-ray diffraction (XRD) can be measured by the same method as described in the above-mentioned calculation method of stacking faults of β-SiC. The measurement is performed by sampling the SiC powder multiple times (e.g., 5 times or more), and the average value is taken as the measured value. The following reference 3 can be cited as a reference document that describes the crystallite size. Reference 3: Yoshio Waseda and Eiichiro Matsubara, "X-ray Structure Analysis: Determining Atomic Arrangement (Materials Science Series)", Uchida Rokakuho, September 30, 1999, 2nd edition, pp. 119-123.

(2. Method for producing SiC powder)
The SiC powder according to the above-described embodiment can be manufactured, for example, by the following manufacturing method.
A step of forming a compact by molding a mixture containing a SiC raw material powder and a powder containing a third element;
sintering the compact at a temperature of 1800° C. or less in an inert atmosphere to obtain a sintered body containing β-SiC;
pulverizing the sintered body to obtain a pulverized sintered body;
A step of classifying the pulverized sintered body to obtain a powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in a cumulative particle size distribution on a volume basis measured by a laser diffraction method;
A method for producing a SiC powder comprising the steps of:

First, a mixture containing SiC raw material powder and a powder containing a third element is molded to produce a molded body. A pore former may be added to the mixture as appropriate. The SiC raw material powder is not particularly limited as long as it is a raw material powder that can produce SiC after sintering, but a typical example is a combination of metal silicon powder and carbonaceous powder. The D50 of the metal silicon powder is preferably 5 μm or more, more preferably 15 μm or more, for the reason of controlling the pore size of the sintered body and making it easy to pulverize. In addition, the D50 of the metal silicon powder is preferably 300 μm or less, more preferably 100 μm or less, for the reason of ease of making a molded body. Therefore, the D50 of the metal silicon powder is preferably 5 to 300 μm, more preferably 15 to 100 μm. The D50 of the metal silicon powder is the particle size at 50% of the cumulative volume in the cumulative particle size distribution on a volume basis measured by a laser diffraction method.

The purity of the metallic silicon powder is preferably 90% by mass or more, more preferably 95% by mass or more. The amount of oxygen in the metallic silicon powder is preferably 3.0% by mass or less, more preferably 1% by mass or less.

The carbonaceous powder may be either crystalline or amorphous, but amorphous carbonaceous powder is preferred, and carbon black is particularly preferred. The carbonaceous powder may be used alone or in combination of two or more types, but amorphous carbonaceous powder is preferred over crystalline carbon (in other words, carbon with a developed crystal structure) such as graphite (i.e., graphite) because it is easy to convert to SiC. The specific surface area of the carbonaceous powder is preferably 30 m ² /g or more, more preferably 50 m ² /g or more, because it is easy to convert to SiC. The specific surface area of the carbonaceous powder is not particularly set as an upper limit, but is usually 2000 m ² /g or less, typically 1000 m ² /g or less, and more typically 200 m ² /g or less. The specific surface area of the carbonaceous powder is measured by a nitrogen adsorption method.

Furthermore, by using a powder containing a third element (typically a metal powder other than metallic silicon), stacking faults in the resulting β-SiC can be reduced. The powder containing a third element preferably contains one or more third elements selected from the group consisting of, but not limited to, Ni, Al, B, N, Ga, Ge, Ti, Cu, Co, P, Cr, and Zr. Of these, it is more preferable that the powder containing a third element contains one or more metallic third elements selected from the group consisting of Ti, Cr, Co, Ni, Al, and Cu.

The purity of the carbonaceous powder is preferably 95% by mass or more, and more preferably 98% by mass or more.

The mixture containing the SiC raw material powder and the third element-containing powder can be obtained, for example, by mixing these powders together with water. For example, it is preferable to mix the carbonaceous powder so that it is 20 to 40 parts by mass, more preferably 25 to 35 parts by mass, and even more preferably 30 to 35 parts by mass, per 100 parts by mass of the metal silicon powder. It is also preferable to mix the third element-containing powder so that it is 1 to 10 atomic numbers in total, more preferably 3 to 8 atomic numbers, and even more preferably 3 to 5 atomic numbers, per 100 atomic numbers of the metal silicon powder. It is also preferable to add 20 to 100 parts by mass of water when the total mass of the metal silicon powder, the carbonaceous powder, and the third element-containing powder is 100 parts by mass.

There are no particular limitations on the mixing method, but for example, a vertical mixer can be used. The resulting mixture is molded by press molding, extrusion molding, or the like to produce a molded body. There are no particular limitations on the shape of the molded body, but examples include cylinders, disks, and square disks. It is preferable to dry the molded body, and it can be dried, for example, at a drying temperature of 50 to 100°C.

The molded body is then fired in an inert atmosphere at a temperature of 1800°C or less to obtain a fired body containing β-SiC. The molded body is preferably fired in an inert atmosphere such as argon or in a vacuum to prevent oxidation. The firing temperature is preferably 1800°C or less, more preferably 1300 to 1500°C, from the viewpoint of suppressing the formation of α-SiC and preferentially forming β-SiC. The firing time can be, for example, 1 to 20 hours. Generally, SiC produced by this method is called reaction sintered SiC. Reaction sintered SiC is SiC produced by utilizing the reaction between raw materials.

The sintered body is preferably porous because it is easy to crush. Specifically, the porosity of the sintered body is preferably 35% or more, more preferably 40% or more, from the viewpoint of ease of crushing. In addition, there is no particular upper limit set for the porosity of the sintered body, but from the viewpoint of ease of production of the molded body and shape retention, it is preferably 80% or less, more preferably 75% or less. Therefore, in one embodiment, the porosity of the sintered body can be 35 to 80%, and preferably 40 to 75%. The porosity of the sintered body can be controlled, for example, by changing the molding pressure. To increase the porosity of the sintered body, a pore-forming material can be added or the molding pressure can be lowered, and conversely, to decrease the porosity of the sintered body, the molding pressure can be increased.

The average pore diameter of the sintered body is preferably 5 μm or more, more preferably 10 μm or more, because it is easy to crush. The average pore diameter of the sintered body is preferably 300 μm or less, more preferably 150 μm or less, because it is easy to flow during molding and a molded body is easily obtained. Therefore, in one embodiment, the average pore diameter of the sintered body can be 5 to 300 μm, and preferably 10 to 150 μm. The average pore diameter of the sintered body can be controlled, for example, by changing the particle size of the raw material metal silicon powder and/or pore-forming material. To increase the average pore diameter of the sintered body, the particle size should be increased, and conversely, to decrease the average pore diameter of the sintered body, the particle size should be decreased.

The sintered body thus obtained is then pulverized to obtain a pulverized sintered body. There are no particular limitations on the pulverization method, but pulverization can be performed, for example, using an impact pulverizer or a mortar. Because pulverization alone does not control the particle size distribution, the pulverized sintered body is classified using a sieve, air classifier, or the like to obtain SiC powder with the desired particle size distribution. In addition to β-SiC, the SiC powder can contain metallic silicon, a third element (typically a metal other than metallic silicon), and a silicide (typically a metallic silicide).

(3. Manufacturing method of electrically heated honeycomb structure)
By using the SiC powder according to the present invention as a raw material, for example, an electrically heated honeycomb structure can be manufactured.
Thus, in one embodiment, the present invention comprises:
a step of forming and drying the clay to obtain a columnar honeycomb formed body having an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall, extending from the first bottom surface to the second bottom surface, and defining a plurality of cells that serve as fluid flow paths;
an electrode portion forming step of applying an electrode portion forming paste to a first region and a second region of a side surface of the honeycomb molded body or a honeycomb fired body obtained by firing the honeycomb molded body, and drying and firing the applied electrode portion forming paste to form a pair of electrode portions;
One or both of the clay and the electrode part forming paste contain the SiC powder according to the present invention described above.
A method for manufacturing an electrically heated honeycomb structure is provided.

(3-1 Manufacturing process of honeycomb formed body)
In this process, the clay is molded and dried to obtain a columnar honeycomb molded body having an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall, extending from the first bottom surface to the second bottom surface, and partitioning a plurality of cells that serve as fluid flow paths. The honeycomb molded body can be manufactured in accordance with a method for manufacturing a honeycomb molded body in a known method for manufacturing a honeycomb structure. For example, a molding raw material is manufactured by mixing a binder, a surfactant, a pore former, water, and the like in addition to ceramic raw materials such as SiC powder (silicon carbide powder) and metal silicon powder. In one embodiment, the SiC powder according to the present invention described above can be used as at least a part of the SiC powder. In another embodiment, only the SiC powder according to the present invention described above can be used as the SiC powder. Note that metal silicon powder needs to be added when the material of the honeycomb structure part is a silicon-silicon carbide composite material, but does not need to be added when the material of the honeycomb structure part is substantially silicon carbide.

The amount of metallic silicon powder is not particularly limited, but can be 15 to 50 parts by mass when the total mass of the SiC powder and metallic silicon powder is 100 parts by mass. The D50 of the metallic silicon powder is not particularly limited, but can be 3 to 50 μm. The D50 of the metallic silicon powder is the particle size at 50% cumulative volume in the cumulative particle size distribution on a volume basis measured by a laser diffraction method. As mentioned above, the D50 of the SiC powder is preferably 8 to 35 μm.

Examples of binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. These may be used alone or in combination of two or more. Of these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The content of the binder is preferably 2 to 15 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass.

The water content is preferably 20 to 60 parts by mass when the total mass of the SiC powder and the 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 content of the surfactant is preferably 0.1 to 2.0 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass.

The pore-forming material is not particularly limited as long as it becomes pores after firing, and examples include graphite, starch, foamed resin, water-absorbent resin, silica gel, etc. These may be used alone or in combination of two or more. The content of the pore-forming material is preferably 0.5 to 10.0 parts by mass when the total mass of the SiC powder and the metal silicon powder is 100 parts by mass. The D50 of the pore-forming material is preferably 10 to 30 μm. The D50 of the pore-forming material means the particle size at 50% of the cumulative volume in the cumulative particle size distribution on a volume basis measured by the laser diffraction method. When the pore-forming material is a water-absorbent resin, the average particle size of the pore-forming material is the average particle size after absorbing water.

Next, the obtained forming raw material is kneaded to form a clay. There are no particular limitations on the method for kneading the honeycomb forming raw material to form a clay, and examples include methods using a kneader, a vacuum clay kneader, etc.

Next, the clay is extruded to produce a honeycomb molded body. In the extrusion molding, a die having a desired overall shape, cell shape, partition wall thickness, cell density, etc. can be used. It is preferable to dry the obtained honeycomb molded body. The honeycomb molded body after drying is sometimes called a "dried honeycomb body". The drying method is not particularly limited, and examples include electromagnetic heating methods such as microwave heating drying and high-frequency dielectric heating drying, and external heating methods such as hot air drying and superheated steam drying. Among these, it is preferable to dry a certain amount of moisture by the electromagnetic heating method and then dry the remaining moisture by the external heating method, in that the entire molded body can be dried quickly and uniformly without cracking. As a drying condition, it is preferable to remove 30 to 99% by mass of moisture from the moisture amount before drying by the electromagnetic heating method, and then reduce the moisture to 3% by mass or less by the external heating method. As the electromagnetic heating method, dielectric heating drying is preferable, and as the external heating method, hot air drying is preferable. Hereinafter, the honeycomb formed body after drying may be referred to as a "dried honeycomb body." If the length in the central axis direction of the honeycomb formed body (dried honeycomb body) is not the desired length, both bottom portions of the honeycomb formed body can be cut to the desired length.

(3-2 Electrode part forming process)
In the electrode portion forming step, an electrode portion forming paste is applied to a first region and a second region of a side surface of the honeycomb molded body or a honeycomb fired body obtained by firing the honeycomb molded body, The electrode part forming paste thus prepared is dried and fired to form a pair of electrodes. The electrode part forming paste preferably contains the SiC powder according to the present invention. More preferably, the powder contains only the SiC powder according to the present invention.

The electrode part forming paste can be prepared by adding additives such as binders, moisturizers, dispersants, water, etc. to the SiC powder and metal silicon powder according to the present invention, and kneading them. Typically, the SiC powder functions as an aggregate, and the metal silicon powder functions as a binder between the aggregates. Metals (metal silicon, metals other than metal silicon) and/or metal silicides that may be contained in the SiC powder also function as binders. The kneading method is not particularly limited, and for example, a vertical mixer can be used.

In order to effectively bond the SiC powder with metallic silicon, the content of metallic silicon powder is preferably 5 to 40 parts by mass, and more preferably 10 to 30 parts by mass, when the total mass of the SiC powder and metallic silicon powder is 100 parts by mass. The D50 of the metallic silicon powder is preferably 1 to 50 μm, and more preferably 4 to 20 μm, to facilitate bonding of the SiC powder with metallic silicon. The D50 of the metallic silicon powder refers to the particle size at 50% of the cumulative volume in the cumulative particle size distribution on a volume basis measured by a laser diffraction method. As mentioned above, the D50 of the SiC powder is preferably 8 to 35 μm.

Examples of binders include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, etc. These may be used alone or in combination of two or more. The content of the binder is preferably 0.1 to 5.0 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass.

An example of a humectant is glycerin. The content of the humectant is preferably 0 to 10 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass.

As dispersants, for example, surfactants such as glycerin, ethylene glycol, dextrin, fatty acid soap, polyalcohol, and polyacrylic acid-based dispersants can be used. These may be used alone or in combination of two or more. The content of the surfactant is preferably 0.1 to 2.0 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass.

The water content is preferably 15 to 60 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass.

In addition, the electrode part forming paste can contain an oxide because it reduces the porosity and thereby reduces the electrical resistivity of the electrode part. The oxide is not particularly limited, but includes oxides of one or more elements selected from the group consisting of B, Mg, Al, Si, P, Ti, Zr, Pb, Li, Na, Ba, Ca, Fe and Sr, and preferably oxides of one or more elements selected from the group consisting of B, Mg, Al, Si, P, Ti and Zr. Among the oxides, oxides of one or more elements selected from the group consisting of Mg, Al and Si are more preferred from the viewpoint of low thermal expansion. Specific examples of oxides include oxides of one element such as MgO, SiO ₂ , and Al ₂ O ₃ , as well as oxides of two or more elements (composite oxides) such as 2MgO·2Al ₂ O ₃ ·5SiO ₂ (cordierite), which is a compound of MgO, SiO ₂ and Al ₂ O ₃ , crystallized glass mainly composed of cordierite such as MgO-SiO-Al ₂ O ₃ -B ₂ O ₃ , and AlTiO ₅ (aluminum titanate), which is a compound of Al ₂ O ₃ and TiO _2. From the viewpoint of improving high temperature durability, it is preferable that at least a part of the oxide in the electrode part is crystalline. One type of oxide may be used alone, or two or more types may be used in combination. When the total volume of the SiC powder and the metal silicon powder is 100 parts by volume, it is preferable that the oxides mentioned above are contained in a total of 1 to 10 parts by volume, and more preferably 1 to 5 parts by volume.

Next, the obtained electrode portion forming paste is applied to the first and second regions of the side surface of the honeycomb formed body or the honeycomb fired body obtained by firing the honeycomb formed body. It is preferable that the electrode portion forming paste is applied so that the first region is located on the opposite side of the center of the honeycomb formed body or the honeycomb fired body to the second region in a cross section of the honeycomb formed body or the honeycomb fired body perpendicular to the extension direction of the cells.

The method for applying the electrode portion forming raw material to the side surface of the honeycomb molded body or the honeycomb fired body obtained by firing the honeycomb molded body is not particularly limited, but for example, a printing method such as screen printing can be used. The coating thickness is not limited, but can be 25 to 500 μm, and typically 75 to 350 μm.

Since only one firing process is required, it is preferable to apply the electrode portion forming paste to the side surface of the dried honeycomb formed body. However, it is also possible to fire the dried honeycomb formed body to produce a honeycomb fired body first, and then apply the electrode portion forming paste to the side surface of this honeycomb fired body. The firing conditions for the honeycomb formed body can be the same as the firing conditions for the electrode portion forming paste described below.

Next, it is preferable to dry the electrode part forming paste applied to the side surface of the honeycomb formed body or the honeycomb fired body. The drying conditions are preferably 50 to 120°C and 1 to 24 hours. After that, the honeycomb formed body with the electrode part forming paste or the honeycomb fired body with the electrode part forming paste is fired to produce a honeycomb structure having a pair of electrodes.

After drying, it is preferable to perform pre-firing before firing to remove binders and the like. For example, pre-firing can be performed in an air atmosphere at 400 to 500°C for 0.5 to 20 hours. As for the conditions for the subsequent firing, it is preferable to heat in an inert atmosphere such as nitrogen or argon at 1350 to 1500°C for 1 to 20 hours. There are no particular limitations on the method of pre-firing and firing, and firing can be performed using an electric furnace, gas furnace, or the like. In addition, after firing, it is preferable to perform oxidation treatment at 1000 to 1350°C for 1 to 10 hours in order to improve durability. The purpose of the oxidation treatment is mainly to oxidize metallic silicon. SiC powder can also be oxidized, but as mentioned above, the SiC powder according to the present invention is not easily oxidized, so the oxidation of the SiC powder by the oxidation treatment is limited.

(4. Electrically heated honeycomb structure)
The structure of the electrically heated honeycomb structure that can be manufactured by the above-mentioned manufacturing method will be described by way of example. Fig. 1 is a perspective view that shows an embodiment of the electrically heated honeycomb structure according to the present invention. The electrically heated honeycomb structure 100 according to the illustrated embodiment includes a columnar honeycomb structure part 110 having an outer peripheral side wall 112, a porous partition wall 118 that is disposed on the inner peripheral side of the outer peripheral side wall 112, extends from a first bottom surface 114 to a second bottom surface 116, and defines a plurality of cells that form a fluid flow path, and at least one electrode part 120 that is joined to the outer surface of the outer peripheral side wall 112 of the columnar honeycomb structure part 110.

Each cell may penetrate from the first bottom surface 114 to the second bottom surface 116 by opening both the first bottom surface 114 and the second bottom surface 116 (flow-through type honeycomb structure). However, from the viewpoint of improving the particulate matter (PM) collection performance when the electrically heated honeycomb structure is used as a filter, it is preferable that the honeycomb structure part 110 has a plurality of first cells extending from the first bottom surface 114 to the second bottom surface 116, with the first bottom surface 114 open and the second bottom surface 116 plugged, and a plurality of second cells extending from the first bottom surface 114 to the second bottom surface 116, with the first bottom surface 114 plugged and the second bottom surface 116 open (wall-flow type honeycomb structure). In this case, the honeycomb structure part 110 can be arranged so that the first cells and the second cells are alternately adjacent to each other with the partition wall 118 between them so that both bottom surfaces have a checkered pattern.

(4-1 Honeycomb structure)
The honeycomb structure part can be formed of ceramics containing one or both of Si (metallic silicon) and SiC (silicon carbide) because it is advantageous for electrical heating. Examples of ceramics containing one or both of Si and SiC include silicon-silicon carbide composites, silicon-oxide composites, silicon carbide-oxide composites, and silicon-silicon carbide-silicon nitride composites. In one embodiment, the SiC constituting the honeycomb structure part is derived from the SiC powder according to the present invention, and in a more preferred embodiment, the SiC constituting the honeycomb structure part is derived substantially only from the SiC powder according to the present invention. In the present invention, even when a columnar honeycomb structure part is formed only from Si, it is called a ceramic as long as it is a sintered body.

Since the columnar honeycomb structure is advantageous for electrical heating, it is more preferable that the total volume ratio of Si and SiC is 60% or more, even more preferable that it is 80% or more, and even more preferable that it is 95% or more.

Other ceramics that can be contained in the honeycomb structure include, but are not limited to, ceramics such as cordierite, mullite, zircon, aluminum titanate, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. These other ceramics may be used alone or in combination of two or more.

From the viewpoint of thermal shock resistance, the thermal expansion coefficient of the honeycomb structure section 110 is preferably 3.5 to 6.0 ppm/K, and more preferably 3.5 to 4.5 ppm/K. In this specification, unless otherwise specified, the thermal expansion coefficient refers to the linear thermal expansion coefficient at 25 to 800°C measured by a method conforming to JIS R1618:2002. As a thermal dilatometer, a "TD5000S (product name)" manufactured by Bruker AXS can be used.

When a voltage is applied between the pair of electrodes, the honeycomb structure is electrically conductive and can generate heat through Joule heat. Therefore, the electrically heated honeycomb structure of the present invention can be suitably used as a heater. The voltage to be applied is preferably 12 to 900 V, but the voltage to be applied can be changed as appropriate.

There are no particular restrictions on the volume resistivity of the honeycomb structure portion, so long as it can generate heat through Joule heat. The volume resistivity of the honeycomb structure portion may be appropriately selected according to the application for which the electrically heated honeycomb structure is used. For example, the volume resistivity of the honeycomb structure portion may be 0.01 to 200 Ωcm, preferably 0.05 to 50 Ωcm, and more preferably 0.1 to 5 Ωcm. The volume resistivity of the honeycomb structure portion here is a value measured at room temperature (25°C) using a four-terminal method.

The partition walls can be porous. In this case, the porosity of the partition walls of the honeycomb structure is not particularly limited, but can be, for example, 35 to 60%, and is preferably 35 to 45%. The porosity is a value measured using a mercury porosimeter.

There are no particular restrictions on the average pore diameter of the partition walls of the honeycomb structure, but it can be, for example, 2 to 15 μm, and preferably 3 to 8 μm. The average pore diameter is a value measured using a mercury porosimeter.

The thickness of the partition walls in the honeycomb structure can be, for example, 0.1 to 0.3 mm, and is preferably 0.1 to 0.15 mm.

The cell density in a cross section perpendicular to the flow path direction of the cells can be, for example, 40 to 150 cells/cm ² , and is preferably 60 to 100 cells/cm ² .

There are no limitations on the shape of the cells in a cross section perpendicular to the flow direction of the cells, but a rectangle, hexagon, octagon, or a combination of these is preferable. Of these, a square and a hexagon are preferable. By using such a cell shape, the pressure loss when exhaust gas flows through the honeycomb structure is reduced, and the purification performance of the catalyst is excellent.

The outer shape of the honeycomb structure part is not particularly limited as long as it is columnar, and may be, for example, a columnar shape with a circular bottom surface (cylindrical shape), a columnar shape with an oval bottom surface, or a columnar shape with a polygonal bottom surface (quadragonal, pentagonal, hexagonal, heptagonal, octagonal, etc.). From the viewpoint of thermal shock resistance, the size of the honeycomb structure part is preferably a bottom area of 2000 to 20000 ^mm2 , and more preferably 4000 to 15000 ^mm2 . From the viewpoint of thermal shock resistance, the length in the central axis direction of the honeycomb structure part is preferably 30 to 200 mm, and more preferably 30 to 120 mm.

(4-2 Electrode part)
The electrically heated honeycomb structure 100 according to this embodiment includes a pair of electrode parts 120 joined to the outer surface of the outer peripheral side wall 112 of the columnar honeycomb structure part 110. In a preferred embodiment, the pair of electrode parts 120 are provided in a band shape extending in the flow path direction of the cells on the outer surface of the outer peripheral side wall 112 of the honeycomb structure part 110, sandwiching the central axis of the honeycomb structure part 110. Thereby, when a voltage is applied between the pair of electrode parts 120, the electrically heated honeycomb structure 100 can suppress bias in the current flowing in the honeycomb structure part 110, and can suppress bias in the temperature distribution in the honeycomb structure part 110. The electrode parts 120 may be provided with terminal connection parts 122 for facilitating connection of terminals.

In one embodiment, the electrode portion has a porous structure in which SiC particles as aggregates are bound by a binder. In a preferred embodiment, the SiC particles constituting the electrode portion are derived from the SiC powder of the present invention, and in a more preferred embodiment, the SiC constituting the electrode portion is substantially derived only from the SiC powder of the present invention. In a preferred embodiment, the binder constituting the electrode portion contains one, two or three types of binders selected from the group consisting of metallic silicon, metals other than metallic silicon, and metallic silicides.

From the viewpoint of improving uniform heat generation, the average thickness of the electrode portion is preferably 25 μm or more, more preferably 50 μm or more, and even more preferably 75 μm or more. From the viewpoint of preventing cracks and peeling due to firing, the average thickness of the electrode portion is preferably 500 μm or less, more preferably 350 μm or less, and even more preferably 250 μm or less. The average thickness of the electrode portion can be calculated by measuring the thickness of the electrode portion at multiple points from an image obtained by imaging a cross section perpendicular to the extension direction of the cells of the electrically heated honeycomb structure using a scanning electron microscope (SEM).

From the viewpoint of improving uniform heat generation, the volume resistivity of the electrode portion is preferably 0.01 to 0.8 Ωcm, and more preferably 0.01 to 0.4 Ωcm. The volume resistivity of the electrode portion can be determined by the four-terminal method.

As shown in FIG. 1, in the electrically heated honeycomb structure 100 of this embodiment, each of the pair of electrode parts 120 is formed in a band shape extending from one bottom surface to the other bottom surface in the flow path direction of the cells of the honeycomb structure part 110. In this way, since the pair of electrode parts 120 are arranged across both bottom surfaces of the honeycomb structure part 110, when a voltage is applied between the pair of electrode parts 120, it is possible to more effectively suppress the bias of the current flowing within the honeycomb structure part 110. And, by suppressing the bias of the current flowing within the honeycomb structure part 110, it is possible to more effectively suppress the bias of the temperature distribution within the honeycomb structure part 110. "Each of the pair of electrode parts 120 is formed in a band shape extending from one bottom surface to the other bottom surface in the cell flow direction of the honeycomb structure part 110" means that one cell flow direction end of each electrode part 120 contacts the peripheral edge of one bottom surface 114 of the honeycomb structure part 110, and the other cell flow direction end of the electrode part 120 contacts the peripheral edge of the other bottom surface 116 of the honeycomb structure part 110.

In one embodiment of the electrically heated honeycomb structure according to the present invention, the electrical resistance can be 100Ω or less. The electrical resistance is measured under the following measurement conditions. Terminals 130 are connected to the center of each electrode section in the cell extension direction and to the center of the honeycomb structure section in the circumferential direction (see FIG. 2). Next, a voltage of 30 V is applied between both terminals, and the resistance value is measured based on the current value 30 seconds later. The electrical resistance is preferably 100Ω or less, more preferably 50Ω or less, and can be, for example, 2 to 40Ω.

(4-3 Use)
The electrically heated honeycomb structure according to the present invention can be used, for example, as a ceramic heater or as a catalyst carrier. The electrically heated honeycomb structure according to the present invention can be used as an EHC by supporting a catalyst. Furthermore, the electrically heated honeycomb structure according to the present invention can also be used as a wall-flow type exhaust gas filter (DPF, GPF, etc.). In this case, a method of using the electrically heated honeycomb structure by passing electricity through it to generate heat during heating for filter regeneration is considered.

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

<1. Production of SiC sintered body>
(SiC sintered body 1)
74.5g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 25.5g of carbon black powder with specific surface area of ^110m2 /g, 7.8g of Ni powder with D50 of 35μm, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was press-molded to produce a cylindrical molded body with a diameter of 25mm and a height of 15mm. Next, the obtained molded body was dried at 100°C, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 2)
73.7g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 26.3g of carbon black powder with specific surface area of ^110m2 /g, 7.7g of Ni powder with D50 of 35μm, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was press molded to produce a cylindrical molded body with φ25mm×H15mm. Next, the obtained molded body was dried at 100°C, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 3)
74.5g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 25.5g of carbon black powder with specific surface area of ^110m2 /g, 4.7g of Ni powder with D50 of 35μm, 4g of methylcellulose, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was extrusion molded to produce a prism-shaped molded body of 25mm x 5mm x 50mm. Next, the obtained molded body was dried at 100°C, degreased in an air atmosphere at 300°C for 5 hours, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 4)
73.7g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 26.3g of carbon black powder with specific surface area of ^110m2 /g, 3.5g of Al powder with D50 of 13μm, 4g of methylcellulose, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was extrusion molded to produce a prism-shaped molded body of 25mm x 5mm x 50mm. Next, the obtained molded body was dried at 100°C, degreased in an air atmosphere at 300°C for 5 hours, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 5)
73.7 g of metallic silicon powder (density 2.33 g/cm ³ ) with D50 of 79 μm, 26.3 g of carbon black powder with specific surface area of 110 m ² /g, 12.0 g of Zr powder with D50 of 11 μm, and 50 g of water were prepared. These were mixed in a planetary stirrer, and the resulting mixed powder was press-molded to produce a cylindrical molded body with a diameter of 25 mm and a height of 15 mm. The resulting molded body was then dried at 100° C., and then fired at 1450° C. in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 6)
73.7g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 26.3g of carbon black powder with specific surface area of ^110m2 /g, 8.3g of Cu powder with D50 of 28μm, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was press-molded to produce a cylindrical molded body with φ25mm×H15mm. Next, the obtained molded body was dried at 100°C, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 7)
73.7g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 26.3g of carbon black powder with specific surface area of ^110m2 /g, 7.7g of Co powder with D50 of 5μm, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was press-molded to produce a cylindrical molded body with a diameter of 25mm and a height of 15mm. Next, the obtained molded body was dried at 100°C, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

(SiC sintered body 8)
73.7g of metal silicon powder (density 2.33g/ ^cm3 ) with D50 of 79μm, 26.3g of carbon black powder with specific surface area of ^110m2 /g, 6.3g of Ti powder with D50 of 20μm, and 50g of water were prepared. These were mixed with a rotating and revolving stirrer to obtain a mixed powder, which was press molded to produce a cylindrical molded body with φ25mm×H15mm. Next, the obtained molded body was dried at 100°C, and then fired at 1450°C in an argon atmosphere for 2 hours to obtain a fired body.

The porosity and average pore diameter of each of the obtained samples of sintered SiC bodies 1 to 8 were measured using a porosimeter (Autopore IV9520 manufactured by Micromeritics). The results are shown in Table 1.

<2. Production of SiC powder>
The obtained SiC sintered bodies 1 to 8 were selected according to the test number shown in Table 2, pulverized, and then classified by an air classifier to obtain SiC powders of Examples and Comparative Examples having the particle size distribution shown in Table 2. The particle size distribution shown in Table 2 was determined based on the cumulative particle size distribution on a volume basis measured by a laser diffraction particle size distribution measuring device LA-950V2 manufactured by HORIBA.

When the type of SiC crystal phase was analyzed by X-ray diffraction (XRD) for each of the SiC powders in the examples and comparative examples, only β-SiC was detected in all cases. In addition, the stacking faults (%) of β-SiC were determined for each of the SiC powders in the examples and comparative examples according to the method described above. The results are shown in Table 2. In addition, when the crystallite size of each of the SiC powders in the examples and comparative examples was determined according to the method described above, all were 1000 Å or more.

The composition of each of the SiC powders in the examples and comparative examples was analyzed by X-ray diffraction (XRD). The composition analysis was performed by pattern fitting using the WPPD (whole-powder-pattern-decomposition) method. The results are shown in Table 2. Nickel silicide was detected in the examples using SiC sintered bodies 1 to 3, aluminum in the example using SiC sintered body 4, zirconium silicide in the example using SiC sintered body 5, copper silicide in the example using SiC sintered body 6, cobalt silicide in the example using SiC sintered body 7, and titanium silicide in the example using SiC sintered body 8.

<3. Manufacturing of Electrically Heated Honeycomb Structure>
(1) Preparation of Electrode Part-Forming Paste 72 g of each of the SiC powders of the Examples and Comparative Examples produced above, 28 g of metallic silicon powder, 1 g of cordierite powder as oxide particles, 1 g of methyl cellulose, 5 g of glycerin, 0.5 g of a polyacrylic acid-based dispersant, and 30 g of water were mixed in a centrifugal mixer to prepare an electrode part-forming paste.

(2) Preparation of honeycomb dried body 6 kg of metal silicon powder, 14 kg of SiC powder, 1 kg of cordierite powder, 1.6 kg of methyl cellulose, and 8 kg of water were mixed and kneaded in a kneader to prepare a honeycomb forming raw material. Next, the obtained honeycomb forming raw material was vacuum kneaded to obtain a clay, and the obtained clay was extrusion molded to obtain a cylindrical honeycomb formed body. The obtained honeycomb formed body was dried at 120°C to obtain a honeycomb dried body.

(3) Preparation of honeycomb structure The electrode part forming paste prepared in advance was applied to the side of the obtained honeycomb dried body with a thickness of 200 μm, and dried at 80° C. to obtain a honeycomb dried body with an electrode forming slurry. The specific coating conditions are as follows. The electrode part forming paste was screen-printed in two places in a band shape over the entire length between both bottom surfaces of the honeycomb dried body so that the central angle defined by two lines connecting both ends of each slurry and the central axis of the honeycomb dried body when the honeycomb dried body is observed at a cross section perpendicular to the flow direction of the cells is 50°. In addition, the electrode part forming pastes at two places were arranged so as to be on opposite sides of the central axis of the honeycomb dried body.

Then, the dried honeycomb body with the electrode part forming paste was degreased, fired, and oxidized to produce an electrically heated honeycomb structure. Degreasing was performed in air at 450°C for 5 hours. Firing was performed in an argon atmosphere at 1450°C for 2 hours. Oxidation was performed in air at 1000°C for 5 hours.

The honeycomb structure part of the obtained electrically heated honeycomb structure had a partition wall thickness of 101.6 μm and a cell density of 93 cells/cm ^2. The diameter of both bottom surfaces of the honeycomb structure part was 100 mm, and the length in the cell extension direction was 100 mm.

(4) Volume resistivity of electrode part A test piece of electrode part having a shape of 5 mm (circumferential direction) × 40 mm (axial direction) × 75 μm (thickness) was taken from the obtained electrically heated honeycomb structure. Then, the electrical resistance at room temperature in a direction perpendicular to the thickness direction of the test piece was measured by a four-terminal method, and the volume resistivity was calculated from the shape of the test piece.
The volume resistivity of the electrode portion was also measured after the honeycomb structure was aged in air at 1300° C. for 50 hours. The rate of change in volume resistivity before and after aging (volume resistivity after aging/volume resistivity before aging) is shown in Table 2. It is problematic that the rate of change in volume resistivity under the assumed usage environment is 2.5 times or more.

Reference Signs List 100 Electrically heated honeycomb structure 110 Honeycomb structure portion 112 Outer peripheral side wall 114 First bottom surface 116 Second bottom surface 118 Partition wall 120 Electrode portion 122 Terminal connection portion

Claims (17)

Contains 70% by mass or more of β-SiC,
A SiC powder for manufacturing an electrically heated honeycomb structure, having a D50 of 8 to 35 μm and a D10 of 5 μm or more in a cumulative particle size distribution on a volume basis measured by a laser diffraction method. The SiC powder according to claim 1, in which the cumulative volume of particles with a particle size of 5 μm or less in the volume-based cumulative particle size distribution measured by a laser diffraction method is 7% or less. The SiC powder according to claim 1 or 2, in which D50 is 15 to 35 μm and D10 is 7 to 20 μm in the cumulative particle size distribution on a volume basis measured by a laser diffraction method. The SiC powder according to any one of claims 1 to 3, in which D90 in the volume-based cumulative particle size distribution measured by a laser diffraction method is 100 μm or less. The SiC powder according to any one of claims 1 to 4, wherein the stacking faults of the β-SiC contained in the powder are 5% or less. The SiC powder according to any one of claims 1 to 5, wherein the stacking faults of the β-SiC contained in the powder are more than 2%. The SiC powder according to any one of claims 1 to 6, further containing one or both of metallic silicon and silicide. The SiC powder according to any one of claims 1 to 7, containing one or more third elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co, P, Cr and Zr. The SiC powder according to claim 8, wherein the total concentration of the third element in the powder is 6 mass% or less. A step of forming a compact by molding a mixture containing a SiC raw material powder and a powder containing one or more third elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co, P, Cr, and Zr;
sintering the compact at a temperature of 1800° C. or less in an inert atmosphere to obtain a sintered body containing β-SiC;
pulverizing the sintered body to obtain a pulverized sintered body;
A step of classifying the pulverized sintered body to obtain a powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in a cumulative particle size distribution on a volume basis measured by a laser diffraction method;
A method for producing a SiC powder comprising the steps of: The method for producing SiC powder according to claim 10, wherein the powder has a cumulative volume of particles with a particle size of 5 μm or less in a volume-based cumulative particle size distribution measured by a laser diffraction method of 7% or less. The method for producing SiC powder according to claim 10 or 11, wherein the powder has a cumulative particle size distribution on a volume basis, measured by a laser diffraction method, of D50 of 15 to 35 μm and D10 of 7 to 20 μm. The method for producing SiC powder according to any one of claims 10 to 12, wherein the powder has a D90 of 100 μm or less in a cumulative particle size distribution based on volume as measured by a laser diffraction method. The method for producing SiC powder according to any one of claims 10 to 13, wherein the porosity of the sintered body is 35 to 80%. The method for producing SiC powder according to any one of claims 10 to 14, wherein the average pore diameter of the sintered body is 5 to 300 μm. a step of forming and drying the clay to obtain a columnar honeycomb formed body having an outer peripheral side wall and partition walls disposed on the inner peripheral side of the outer peripheral side wall, extending from the first bottom surface to the second bottom surface, and defining a plurality of cells that serve as fluid flow paths;
an electrode portion forming step of applying an electrode portion forming paste to a first region and a second region of a side surface of the honeycomb molded body or a honeycomb fired body obtained by firing the honeycomb molded body, and drying and firing the applied electrode portion forming paste to form a pair of electrode portions;
One or both of the clay and the electrode part forming paste contain the SiC powder according to any one of claims 1 to 9.
A method for manufacturing an electrically heated honeycomb structure. An electrically heated honeycomb structure containing the SiC powder according to any one of claims 1 to 9.