WO2020246004A1

WO2020246004A1 - Sic powder and manufacturing method thereof, honeycomb structure of electrical heating type and manufacturing method thereof

Info

Publication number: WO2020246004A1
Application number: PCT/JP2019/022634
Authority: WO
Inventors: 貴文木俣; 宗一郎青柳; 規介山本
Original assignee: 日本碍子株式会社
Priority date: 2019-06-06
Filing date: 2019-06-06
Publication date: 2020-12-10

Abstract

SiC powder with electrical resistivity that is unlikely to increase with time and a manufacturing method thereof are provided. The SiC powder includes 70% by mass or more of β-SiC, and has a D50 of 8-35 μm and a D10 of 5 μm or more in a volume-based cumulative particle size distribution measured by a laser diffraction method.

Description

SiC powder and its manufacturing method, electrically heated honeycomb structure and its manufacturing method

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

Conventionally, a ceramic honeycomb structure has been used as a base material for an electric heating catalyst (EHC) for purifying exhaust gas and a ceramic heater. In such an application, a metal terminal is connected to a pair of electrode portions of the honeycomb structure, and a voltage is applied to heat the honeycomb structure. For example, the EHC is an exhaust purification device provided in an exhaust path of an automobile or the like to purify the exhaust gas discharged from the engine. A catalyst is supported on this EHC, and by heating the EHC, the catalyst is heated to a temperature required for activation.

Conventionally, a technique focusing on the electrical resistivity of the electrode portion has been known in order to improve the uniformity of the current flowing through the EHC. In Japanese Patent Application Laid-Open No. 2014-198320 (Patent Document 1), the electrode portion is made of a porous body in which particles made of silicon carbide as an aggregate are bonded by a binder, and the electrode portion is used as the aggregate constituting the electrode portion. It is proposed that the silicon carbide of Silicon Carbide contains β-SiC having a stacking defect of 2% or less, and the binder constituting the electrode portion contains silicon and a metal siliceous product. Patent Document 1 describes that the electrical resistivity of the electrode portion can be made lower than that of the electrode portion of the conventional honeycomb structure by the configuration. Then, it is described that the current supplied to one of the pair of electrode portions is satisfactorily transmitted to the entire area of the electrode portion, and the current flows uniformly from the electrode portion to the entire honeycomb structure. Has been done.

Further, in paragraph 0047 of Patent Document 1, "The average particle size of the particles made of silicon carbide as an aggregate is preferably 10 to 70 μm, more preferably 10 to 50 μm, and 15 to 40 μm. When the average particle diameter of the particles made of silicon carbide contained in the electrode portion is less than 10 μm, the electric resistance of the electrode portion tends to be high, and the silicon carbide contained in the electrode portion tends to be high. When the average particle size of the particles made of silicon is more than 70 μm, the strength of the electrode portion tends to decrease. ”

JP-A-2014-1983320

Patent Document 1 discloses a technical idea of lowering the electrical resistivity of the electrode portion in order to allow current to flow uniformly throughout the honeycomb structure. Then, in order to reduce the electrical resistivity of the electrode portion, β-SiC having a stacking defect of 2% or less is used as the aggregate constituting the electrode portion, and the average particle diameter of the aggregate particles is set to 10 to 70 μm. It is specifically proposed to control.

However, Patent Document 1 lacks consideration of changes in electrical resistivity over time, and even if a low electrical resistivity is initially obtained, there is a concern that the electrical resistivity will increase if it is used for a long period of time. there were. According to the results of the study by the present inventor, it has been found that β-SiC described in Patent Document 1 tends to increase the electrical resistivity due to long-term use and may reduce the heating performance of the honeycomb structure. .. Therefore, it is desirable to provide an electrically heated honeycomb structure in which the electrical resistivity does not easily increase even after long-term use.

In view of the above circumstances, it is an object of the present invention to provide a SiC powder whose electrical resistivity does not easily increase with time and a method for producing the same in one embodiment. An object of the present invention is to provide, in another embodiment, an electrically heated honeycomb structure manufactured by 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 D50 of 8 to 35 μm and a D10 of 5 μm or more in a volume-based cumulative particle size distribution 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 the 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 the volume-based cumulative particle size distribution measured by the laser diffraction method.
[4]
The SiC powder according to any one of [1] to [3], wherein D90 in the 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 β-SiC stacking defect contained in the powder is 5% or less.
[6]
The SiC powder according to any one of [1] to [5], wherein the β-SiC stacking defect contained in the powder is more than 2%.
[7]
The SiC powder according to any one of [1] to [6], which further contains one or both of metallic silicon and metallic silicide.
[8]
Any one of [1] to [7] containing one or more metal elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co and Zr. The SiC powder according to.
[9]
The SiC powder according to [8], wherein the total concentration of the metal elements in the powder is 6% by mass or less.
[10]
A process of molding a mixture containing a SiC raw material powder and a metal powder to prepare a molded product, and
A step of firing the molded product at a temperature of 1800 ° C. or lower in an inert atmosphere to obtain a fired product containing β-SiC.
A step of crushing the fired body to obtain a crushed fired body, and
A step of classifying the crushed fired body to obtain a powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in the volume-based cumulative particle size distribution measured by a laser diffraction method.
A method for producing a SiC powder containing.
[11]
The method for producing SiC powder according to [10], wherein the powder has an integrated 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 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 metal powder contains one or more metal particles selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co and Zr [10] to [13]. The method for producing SiC powder according to any one of the above.
[15]
The method for producing SiC powder according to any one of [10] to [14], wherein the fired body has a porosity of 35 to 80%.
[16]
The method for producing SiC powder according to any one of [10] to [15], wherein the fired body has an average pore diameter of 5 to 300 μm.
[17]
By forming and drying the clay, the outer peripheral side wall and a plurality of cells which are arranged on the inner peripheral side of the outer peripheral side wall and extend from the first bottom surface to the second bottom surface to serve as a fluid flow path are formed. The process of obtaining a columnar honeycomb molded body having a partition wall,
The electrode portion forming paste is applied to the first region and the second region of the side surface of the honeycomb molded product or the honeycomb molded product obtained by firing, respectively, and the electrode portion is formed. A step of forming an electrode portion by drying and firing the paste to form a pair of electrode portions is provided.
One or both of the clay and the electrode portion-forming paste contains 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 production method according to [17].
[19]
An electrically heated honeycomb structure containing the SiC powder according to any one of [1] to [9].

According to one embodiment of the present invention, there is provided a SiC powder whose electrical resistivity does not easily increase with time and a method for producing the same. 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 having excellent durability and whose electrical resistance does not easily increase even after long-term use.

It is a perspective view which shows typically one Embodiment of the honeycomb structure which concerns on this invention. It is a schematic diagram explaining the method of measuring the energization resistance.

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

(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 volume-based cumulative particle size distribution measured by the 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, the SiC powder according to the present invention has a D50 of 8 to 35 μm and a D10 of 5 μm or more in the volume-based cumulative particle size distribution measured by the laser diffraction method. Preferably, D50 is 15-35 μm and D10 is 7-20 μm. More preferably, D50 is 20 to 30 μm and D10 is 12 to 20 μm. D50 is a particle size of 50% of the cumulative volume in the cumulative particle size distribution measured above. D10 is a particle size of 10% of the cumulative volume in the cumulative particle size distribution measured above. When the D50 of the SiC powder is 8 μm or more and the D10 is 5 μm or more, the oxidation of SiC is suppressed and the electrical resistivity of the SiC powder itself is less likely to increase with time, and this is produced as a raw material powder. An advantage is obtained that an increase in the electrical resistivity of the fired body over time is suppressed. Further, when D10 is 20 μm or less and D50 is 35 μm or less, moldability can be ensured.

In one embodiment, the SiC powder according to the present invention has an integrated 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 of 7% or less. In addition to D50 and D10, the small integrated volume of particles having a particle size of 5 μm or less further suppresses the oxidation of SiC, further improving the effect of making it difficult for the electrical resistivity of the SiC powder itself to increase over time. It is possible to obtain an advantage that an increase in the electrical resistivity of the fired product produced using the above as a raw material powder with time is further suppressed. The integrated volume of particles having 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, the SiC powder according to the present invention has a D90 of 100 μm or less in a volume-based cumulative particle size distribution measured by a laser diffraction method. 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 is a particle size of 90% of the cumulative volume in the cumulative particle size distribution measured above.

(1-2 SiC powder composition)
In one embodiment, the SiC powder according to the present invention contains 70% by mass or more of β-SiC. Since the SiC powder contains β-SiC as a main component, the initial electrical resistivity of the SiC powder itself can be suppressed to a low level, and the initial electrical resistivity of a fired product produced using this as a raw material powder can be lowered. it can. 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 concentration of β-SiC in the SiC powder, and it can be substantially 100% by mass. However, in order to suppress stacking defects, a metal element described later may be added, or unreacted raw materials remain. In consideration of the above, 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 metallic silicide. Metallic silicon is not particularly required, but metallic silicon used as a raw material for SiC powder may remain. Further, the metal silicide can be formed by reacting a metal described later, which is added to suppress a stacking defect of β-SiC, with metallic silicon used as a raw material for SiC powder.

In one embodiment, the SiC powder according to the present invention contains one or more metal elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co and Zr. .. Among these, it is more preferable to contain one or more metal elements selected from the group consisting of Ni, Al and Cu. These metal elements contribute to suppressing the initial electrical resistivity of the SiC powder itself by suppressing the stacking defects of β-SiC, and the initial electrical resistance of the fired product produced using this as the raw material powder. It can contribute to keeping the rate low.

In order to enhance the effect of suppressing stacking defects of β-SiC, the total concentration of the metal elements in the SiC powder is preferably 1% by mass or more, and more preferably 3% by mass or more. On the other hand, if the concentration of the metal element in the SiC powder becomes too high, the coefficient of thermal expansion of the fired body produced using the SiC powder as the raw material powder may increase. Therefore, the total concentration of the metal elements in the SiC powder is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 6% by mass or less.

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

Here, the stacking defect of β-SiC will be described. First, a stacking defect is a kind of planar lattice defect (plane defect), and when it is considered that a perfect crystal is formed by periodic stacking of atomic planes, the regularity (order) of this stacking is disturbed. It means that is occurring. In the present specification, the stacking defect (%) of β-SiC refers to a value calculated by the following formula (1). Here, A in the following (1) is a value calculated by the following formula (2).

The "33.6 ° peak intensity" in the formula (2) is the peak intensity when the scattering angle (2θ) is 33.6 ° in the X-ray diffraction spectrum by X-ray diffraction (XRD). Further, "41.4 ° peak intensity" is the peak intensity when the scattering angle (2θ) is 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 with CuKα rays having 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 light receiving slit (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, and “A” is calculated by the above equation (2). Then, according to the above formula (1), the stacking defect of β-SiC can be obtained. The measurement is performed by sampling the SiC powder a plurality of times (eg, 5 times or more), and the average value is used as the measured value. References 1 and 2 below can be mentioned as references describing the stacking defects of β-SiC. Reference 1: Journal of the Ceramic Society of Japan 99 [12], p1179-1184 (1991). Reference 2: Journal of the Ceramic Society of Japan, 106 [5], p483-487, (1998).

(1-4 β-SiC crystallite size)
The crystallite size of β-SiC is preferably 900 Å or more, more preferably 900 to 500,000 Å, and particularly preferably 1000 to 500,000 Å. The crystallite size of β-SiC refers to a value calculated by the following formula (3). The following equation (3) is Scheller's equation. Usually, one crystal grain is composed of fine crystals that can be regarded as a plurality of single crystals, and these fine crystals are called crystallites. The size of this crystallite is the above-mentioned "crystallite size". When 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 fired product produced using this as a raw material powder is satisfactorily lowered. Can be made to.

“T (Å)” in the formula (3) indicates the crystallite size (Å). “Λ” indicates the X-ray wavelength (1.54 Å). “B” indicates the half width of the peak having a scattering angle (2θ) of 35.6 °. “Θ _B ” is a value of 1/2 of 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-described method for calculating β-SiC stacking defects. The measurement is performed by sampling the SiC powder a plurality of times (eg, 5 times or more), and the average value is used as the measured value. Reference 3 below can be mentioned as a reference describing the crystallite size. Reference 3: Yoshio Waseda and Eiichiro Matsubara, "X-ray structure analysis: Determining the arrangement of atoms (material science series)", Ryozuru Uchida, September 30, 1999, 2nd edition, p119-123.

(2. Method for manufacturing SiC powder)
The SiC powder according to the above-described embodiment can be produced, for example, by the following production method.
A process of molding a mixture containing a SiC raw material powder and a metal powder to prepare a molded product, and
A step of firing the molded product at a temperature of 1800 ° C. or lower in an inert atmosphere to obtain a fired product containing β-SiC.
A step of crushing the fired body to obtain a crushed fired body, and
A step of classifying the crushed fired body to obtain a powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in a volume-based cumulative particle size distribution measured by a laser diffraction method.
A method for producing a SiC powder containing.

First, a mixture containing SiC raw material powder and metal powder is molded to prepare a molded product. A pore-forming material 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 capable of producing SiC after firing, but a combination of metallic silicon powder and carbonaceous powder is typically used. The D50 of the metallic silicon powder is preferably 5 μm or more, more preferably 15 μm or more, because it controls the pore size of the fired body and facilitates pulverization. The D50 of the metallic silicon powder is preferably 300 μm or less, more preferably 100 μm or less, for the reason of ease of forming a molded product. Therefore, the D50 of the metallic silicon powder is preferably 5 to 300 μm, more preferably 15 to 100 μm. D50 of the metallic silicon powder is a particle size of 50% of the cumulative volume in the volume-based cumulative particle size distribution measured by the 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 3.0% by mass, more preferably 1% by mass or less.

The carbonaceous powder may be either crystalline or amorphous, but amorphous carbonaceous powder is preferable, and carbon black is particularly preferable. The carbonaceous powder may be used alone or in combination of two or more, but the carbonaceous powder is such as graphite (that is, graphite) because it is easily converted into SiC. Amorphous carbonaceous powder is preferable to crystalline carbon (in other words, carbon having a well-developed crystal structure). The specific surface area of the carbonaceous powder is preferably 30 m ² / g or more, and more preferably 50 m ² / g or more because it is easily converted into SiC. The specific surface area of the carbonaceous powder is not particularly set, 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. is there. The specific surface area of the carbonaceous powder is measured by the nitrogen adsorption method.

Further, by using a metal powder other than metallic silicon, it is possible to reduce the stacking defects of β-SiC to be generated. The metal powder may contain one or more metal particles selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co and Zr, but not limited to. preferable. Among these, the metal powder more preferably contains one or more metal particles selected from the group consisting of Ni, Al and Cu.

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

A mixture containing a SiC raw material powder and a metal powder can be obtained, for example, by mixing these powders with water. Illustratively, it is preferable to mix the carbonaceous powder so as to be 20 to 40 parts by mass, and more preferably 25 to 35 parts by mass with respect to 100 parts by mass of the metallic silicon powder. It is even more preferable to mix the mixture so as to have 30 to 35 parts by mass. Further, it is preferable to mix metal powders other than metallic silicon so as to have 1 to 10 atomic numbers with respect to 100 atomic numbers of metallic silicon powder, and more preferably to mix so as to have 3 to 8 atomic numbers. It is even more preferable to mix them so that the number of atoms is 3 to 5. Further, when the total mass of the metallic silicon powder, the carbonaceous powder, and the metal powder other than the metallic silicon is 100 parts by mass, it is preferable to add 20 to 100 parts by mass of water.

The mixing method is not particularly limited, but for example, a vertical stirrer can be used. The obtained mixture is molded by press molding, extrusion molding or the like to prepare a molded product. The shape of the molded product is not particularly limited, and examples thereof include a cylinder, a disk, and a square disk. The molded product is preferably dried, for example, it can be dried at a drying temperature of 50 to 100 ° C.

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

The fired body is preferably porous because it is easy to crush. Specifically, the porosity of the fired body is preferably 35% or more, and more preferably 40% or more, from the viewpoint of ease of pulverization. Further, although the upper limit of the porosity of the fired body is not particularly set, it is preferably 80% or less, and more preferably 75% or less, from the viewpoint of ease of manufacturing the molded body and shape retention. Therefore, in one embodiment, the porosity of the fired body can be 35% to 80%, preferably 40 to 75%. The porosity of the fired body can be controlled, for example, by a method of changing the molding pressure. To increase the porosity of the fired body, a pore-forming material may be added or the molding pressure may be lowered, and conversely, to reduce the porosity of the fired body, the molding pressure may be increased.

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

Next, the fired body thus obtained is crushed to obtain a crushed fired body. The crushing method is not particularly limited, but crushing can be performed by, for example, an impact crusher or a mortar. Since the particle size distribution is not controlled only by crushing, the crushed fired body is classified by a sieve, an air classifier, or the like to obtain a SiC powder having a desired particle size distribution. In addition to β-SiC, the SiC powder may contain metallic silicon, metals other than metallic silicon, and metal 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.
Therefore, in one embodiment, the present invention
By forming and drying the clay, the outer peripheral side wall and a plurality of cells which are arranged on the inner peripheral side of the outer peripheral side wall and extend from the first bottom surface to the second bottom surface to serve as a fluid flow path are formed. The process of obtaining a columnar honeycomb molded body having a partition wall,
The electrode portion forming paste is applied to the first region and the second region of the side surface of the honeycomb molded product or the honeycomb molded product obtained by firing, respectively, and the electrode portion is formed. A step of forming an electrode portion by drying and firing the paste to form a pair of electrode portions is provided.
One or both of the clay and the electrode portion-forming paste contains the SiC powder according to the present invention described above.
Provided is a method for manufacturing an electrically heated honeycomb structure.

(3-1 Manufacturing process of honeycomb molded product)
In this step, by molding and drying the clay, a plurality of cells are arranged on the outer peripheral side wall and the inner peripheral side of the outer peripheral side wall, extend from the first bottom surface to the second bottom surface, and serve as a fluid flow path. A columnar honeycomb molded body having a partition forming a partition is obtained. The honeycomb molded body can be produced according to the method for producing a honeycomb molded body in the known method for producing a honeycomb structure. For example, first, in addition to ceramic raw materials such as SiC powder (silicon carbide powder) and metallic silicon powder, a binder, a surfactant, a pore-forming material, water, and the like are mixed to prepare a molding raw material. In one embodiment, the above-mentioned SiC powder according to the present invention can be used as at least a part of the SiC powder. Further, in another embodiment, only the SiC powder according to the present invention described above can be used as the SiC powder. The metallic silicon powder needs to be added when the material of the honeycomb structure is a silicon-silicon carbide composite material, but is added when the material of the honeycomb structure is substantially silicon carbide. There is no need.

The content of the 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 the 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. D50 of the metallic silicon powder is a particle size of 50% of the cumulative volume in the volume-based cumulative particle size distribution measured by the laser diffraction method. As described above, the D50 of the SiC powder is preferably 8 to 35 μm.

Examples of the binder include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol and the like. These may be used individually by 1 type, or may be used in combination of 2 or more type. Among these, it is preferable to use methyl cellulose and hydroxypropoxyl cellulose in combination. The binder content 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.

As the surfactant, ethylene glycol, dextrin, fatty acid soap, polyalcohol and the like can be used. These may be used individually by 1 type, or may be used in combination of 2 or more type. 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 thereof include graphite, starch, foamed resin, water-absorbent resin, and silica gel. These may be used individually by 1 type, or may be used in combination of 2 or more type. 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 metallic silicon powder is 100 parts by mass. The D50 of the pore-forming material is preferably 10 to 30 μm. D50 of the pore-forming material means a particle size of 50% of the cumulative volume in the volume-based cumulative particle size distribution measured by the laser diffraction method. When the pore-forming material is a water-absorbent resin, the average particle diameter of the pore-forming material is the average particle diameter after water absorption.

Next, the obtained molding raw material is kneaded to form a clay. The method of kneading the honeycomb molding raw materials to form the clay is not particularly limited, and examples thereof include a method using a kneader, a vacuum clay kneader, and the like.

Next, 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. It is preferable to dry the obtained honeycomb molded product. The dried honeycomb molded body may be referred to as a "honeycomb dried body". The drying method is not particularly limited, and examples thereof include an electromagnetic wave heating method such as microwave heating drying and high frequency dielectric heating drying, and an external heating method such as hot air drying and superheated steam drying. Among these, the entire molded product can be dried quickly and uniformly without cracking, and after drying a certain amount of water by the electromagnetic wave heating method, the remaining water is dried by the external heating method. It is preferable to let it. As a condition for drying, it is preferable that after removing 30 to 99% by mass of water with respect to the amount of water before drying by an electromagnetic wave heating method, the water content is reduced to 3% by mass or less by an external heating method. As the electromagnetic wave heating method, dielectric heating drying is preferable, and as the external heating method, hot air drying is preferable. Hereinafter, the dried honeycomb molded body may be referred to as a “honeycomb dried body”. When the length in the central axis direction of the honeycomb molded body (honeycomb dried body) is not the desired length, both bottom portions of the honeycomb molded body can be cut to obtain the desired length.

(3-2 Electrode part forming process)
In the electrode portion forming step, the electrode portion forming paste is applied and applied to the first region and the second region of the side surface of the honeycomb molded product or the honeycomb molded product obtained by firing the honeycomb molded product, respectively. The processed electrode portion forming paste is dried and fired to form a pair of electrode portions. The electrode portion forming paste preferably contains the SiC powder according to the present invention. Further, as the SiC powder in the electrode portion forming paste, it is more preferable to contain only the SiC powder according to the present invention.

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

In order to effectively bond the SiC powder with metallic silicon, the content of the metallic silicon powder is preferably 5 to 40 parts by mass when the total mass of the SiC powder and the metallic silicon powder is 100 parts by mass. More preferably, it is 10 to 30 parts by mass. Further, the D50 of the metallic silicon powder is preferably 1 to 50 μm, and more preferably 4 to 20 μm, for the reason that the SiC powder can be easily bonded with the metallic silicon. D50 of the metallic silicon powder means a particle size of 50% of the cumulative volume in the volume-based cumulative particle size distribution measured by the laser diffraction method. As described above, the D50 of the SiC powder is preferably 8 to 35 μm.

Examples of the binder include methyl cellulose, hydroxypropyl methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol and the like. These may be used individually by 1 type, or may be used in combination of 2 or more type. The binder content 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.

Glycerin can be mentioned as a moisturizer. The content of the moisturizer 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 the dispersant, for example, glycerin, ethylene glycol, dextrin, fatty acid soap, polyalcohol, polyacrylic acid-based dispersant and the like can be used as the surfactant. These may be used individually by 1 type, or may be used in combination of 2 or more type. 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 portion-forming paste can contain an oxide because it lowers the porosity and thereby lowers the electrical resistivity of the electrode portion. The oxide is not particularly limited, but one or two selected from the group consisting of B, Mg, Al, Si, P, Ti, Zr, Pb, Li, Na, Ba, Ca, Fe and Sr. Oxides of the above elements can be mentioned, 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 preferable 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 ₂ MgO, 2Al ₂ O ₃ , which are compounds of MgO, SiO _2, and Al ₂ O _3. Crystallized glass containing elementite as a main component, such as 5SiO ₂ (corgerite) and MgO-SiO-Al ₂ O _3- B ₂ O ₃ , Al TiO ₅ (titanium), which is a compound of Al ₂ O ₃ and TiO _2. Oxides (composite oxides) of two or more elements such as aluminum acid) can be mentioned. From the viewpoint of enhancing high temperature durability, it is preferable that at least a part of the oxide in the electrode portion 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 metallic silicon powder is 100 parts by volume, the above oxides are preferably 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 region and the second region of the side surface of the honeycomb molded body or the honeycomb molded body obtained by firing the honeycomb molded body, respectively. The electrode portion forming paste has a cross section orthogonal to the extending direction of the cell of the honeycomb molded body or the honeycomb fired body, and the first region is the honeycomb molded body or the honeycomb with respect to the second region. It is preferable to apply the coating so that it is located on the opposite side of the center of the fired body.

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

Since only one firing step is required, it is preferable to apply the electrode portion forming paste to the side surface of the dried honeycomb molded body. However, it is also possible to fire the dried honeycomb molded body to prepare the honeycomb fired body first, and then apply the electrode portion forming paste to the side surface of the honeycomb fired body. As the firing conditions of the honeycomb molded body, the same conditions as the firing conditions of the electrode portion forming paste described later can be adopted.

Next, it is preferable to dry the electrode portion forming paste coated on the side surface of the honeycomb molded body or the honeycomb fired body. The drying conditions are preferably 50 to 120 ° C. and 1 to 24 hours. Then, by firing the honeycomb molded body with the electrode portion forming paste or the honeycomb fired body with the electrode portion forming paste, a honeycomb structure having a pair of electrode portions can be produced.

It is preferable to perform temporary firing in order to remove binders and the like after drying and before firing. Illustratively, the calcination can be carried out in an air atmosphere at 400 to 500 ° C. for 0.5 to 20 hours. Subsequent firing conditions are preferably 1350 to 1500 ° C. for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. The method of tentative firing and firing is not particularly limited, and firing can be performed using an electric furnace, a gas furnace, or the like. Further, after firing, it is preferable to carry out an 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. The SiC powder can also be oxidized, but as described above, since the SiC powder according to the present invention is difficult to be oxidized, the oxidation of the SiC powder by the oxidation treatment is limited.

(4. Electric heating type honeycomb structure)
The structure of the electrically heated honeycomb structure that can be manufactured by the above-mentioned manufacturing method will be exemplified. FIG. 1 is a perspective view schematically showing an embodiment of an electrically heated honeycomb structure according to the present invention. The electrically heated honeycomb structure 100 according to the illustrated embodiment is arranged on the outer peripheral side wall 112 and the inner peripheral side of the outer peripheral side wall 112, and extends from the first bottom surface 114 to the second bottom surface 116 to flow a fluid flow path. A columnar honeycomb structure 110 having a porous partition wall 118 for partitioning a plurality of cells to be formed, and at least one electrode portion 120 joined to the outer surface of the outer peripheral side wall 112 of the columnar honeycomb structure 110. Be prepared.

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 collection performance of granular substances (PM) when the electrically heated honeycomb structure is used as a filter, the honeycomb structure portion 110 extends from the first bottom surface 114 to the second bottom surface 116, and is first. A plurality of first cells in which the bottom surface 114 is opened and the second bottom surface 116 is sealed, and the first bottom surface 114 extends from the first bottom surface 114 to the second bottom surface 116, and the first bottom surface 114 is sealed and the second bottom surface 116 is sealed. It is preferable to have a plurality of second cells to be opened (wall flow type honeycomb structure). In this case, in the honeycomb structure 110, the first cell and the second cell can be alternately arranged adjacent to each other with the partition wall 118 so that both bottom surfaces have a checkered pattern.

(4-1 Honeycomb structure)
Since the honeycomb structure is advantageous for electric heating, it can be formed of ceramics containing one or both of Si (metal silicon) and SiC (silicon carbide). Examples of ceramics containing one or both of Si and SiC include silicon-silicon carbide composite material, silicon-oxide composite material, silicon carbide-oxide composite material, and silicon-silicon carbide-silicon nitride composite material. Be done. In one embodiment, the SiC constituting the honeycomb structure is derived from the SiC powder according to the present invention, and in a more preferable embodiment, the SiC constituting the honeycomb structure is substantially derived only from the SiC powder according to the present invention. .. In the present invention, even when the columnar honeycomb structure is formed only of Si, it is referred to as ceramic as long as it is a sintered body.

Since the columnar honeycomb structure is advantageous for electric heating, the total volume ratio of Si and SiC is more preferably 60% or more, further preferably 80% or more, and even more preferably 95% or more. Is even more preferable.

Other ceramics that can be contained in the honeycomb structure are not limited, but are ceramics such as cordierite, mullite, zirconate, aluminum titanate, silicon nitride, zirconia, spinel, indialite, sapphirine, corundum, and titania. Can be mentioned. As for these other ceramics, only one kind may be used, or two or more kinds may be used in combination.

The coefficient of thermal expansion of the honeycomb structure 110 is preferably 3.5 to 6.0 ppm / K, more preferably 3.5 to 4.5 ppm / K, from the viewpoint of thermal shock resistance. In the present specification, the coefficient of thermal expansion refers to a coefficient of linear thermal expansion of 25 to 800 ° C. measured by a method according to JIS R1618: 2002, unless otherwise specified. As the thermal expansion meter, "TD5000S (trade name)" manufactured by BrukerAXS can be used.

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

There is no particular limitation on the volume resistivity of the honeycomb structure as long as it can generate heat due to Joule heat. The volume resistivity of the honeycomb structure may be appropriately selected according to the application in which the electrically heated honeycomb structure is used. Illustratively, the volume resistivity of the honeycomb structure can be 0.01 to 200 Ωcm, preferably 0.05 to 50 Ωcm, and even 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.) by the 4-terminal method.

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

The average pore diameter of the partition wall of the honeycomb structure is not particularly limited, but can be, for example, 2 to 15 μm, preferably 3 to 8 μm. The average pore diameter is a value measured by a mercury porosimeter.

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

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

There is no limitation on the shape of the cell in the cross section orthogonal to the flow path direction of the cell, but it is preferably a quadrangle, a hexagon, an octagon, or a combination thereof. Of these, squares and hexagons are preferred. By making the cell shape in this way, the pressure loss when the exhaust gas is passed through the honeycomb structure portion is reduced, and the purification performance by the catalyst is excellent.

The outer shape of the honeycomb structure is not particularly limited as long as it is columnar. For example, the bottom surface is a circular columnar shape (cylindrical shape), the bottom surface is an oval-shaped columnar shape, and the bottom surface is a polygonal shape (quadrangle, pentagon, hexagon, heptagon, octagon). It can have a columnar shape (such as a polygon). Also, the size of the honeycomb structure portion, in view of thermal shock resistance, it is preferable that the area of the bottom is 2000 ~ 20000 mm ^2, further preferably 4000 ~ 15000 ^2. Further, the length of the honeycomb structure portion in the central axis direction is preferably 30 to 200 mm, more preferably 30 to 120 mm, from the viewpoint of thermal shock resistance.

(4-2 Electrode part)
The electrically heated honeycomb structure 100 according to the present embodiment includes a pair of electrode portions 120 joined to the outer surface of the outer peripheral side wall 112 of the columnar honeycomb structure portion 110. In a preferred embodiment, a pair of electrode portions 120 are extended in a band shape in the cell flow path direction on the outer surface of the outer peripheral side wall 112 of the honeycomb structure portion 110 with the central axis of the honeycomb structure portion 110 interposed therebetween. As a result, the electrically heated honeycomb structure 100 can suppress the bias of the current flowing in the honeycomb structure 110 when a voltage is applied between the pair of electrode portions 120, and the temperature distribution in the honeycomb structure 110 can be suppressed. It is possible to suppress the bias of. The electrode unit 120 may be provided with a terminal connection unit 122 for facilitating terminal connection.

In one embodiment, the electrode portion has a porous structure in which SiC particles as an aggregate are bonded by a binder. In a preferred embodiment, the SiC particles constituting the electrode portion are derived from the SiC powder according to the present invention, and in a more preferred embodiment, the SiC constituting the electrode portion is substantially derived only from the SiC powder according to the present invention. Further, in a preferred embodiment, the binder constituting the electrode portion contains one, two or three types of binder selected from the group consisting of metallic silicon, a metal other than metallic silicon, and metal silicide.

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 enhancing uniform heat generation. Further, the average thickness of the electrode portion is preferably 500 μm or less, more preferably 350 μm or less, still more preferably 250 μm or less, from the viewpoint of preventing cracks and peeling due to firing. The average thickness of the electrode portion is calculated by measuring the thickness of the electrode portion at a plurality of locations from an image obtained by imaging a cross section of the electrically heated honeycomb structure perpendicular to the extending direction of the cell with a scanning electron microscope (SEM). can do.

The volume resistivity of the electrode portion is preferably 0.01 to 0.8 Ωcm, more preferably 0.01 to 0.4 Ωcm, from the viewpoint of enhancing uniform heat generation. The volume resistivity of the electrode portion can be obtained by the 4-terminal method.

As shown in FIG. 1, in the electrically heated honeycomb structure 100 of the present embodiment, each of the pair of electrode portions 120 is from one bottom surface to the other bottom surface in the flow path direction of the cell of the honeycomb structure portion 110. It is formed in an extending band shape. In this way, the pair of electrode portions 120 are arranged between both bottom surfaces of the honeycomb structure portion 110, so that when a voltage is applied between the pair of electrode portions 120, the current flows through the honeycomb structure portion 110. The bias of the current can be suppressed more effectively. Then, by suppressing the bias of the current flowing in the honeycomb structure 110, the bias of the temperature distribution in the honeycomb structure 110 can be suppressed more effectively. "Each of the pair of electrode portions 120 is formed in a band shape extending from one bottom surface to the other bottom surface in the direction of the cell flow path of the honeycomb structure portion 110" means that one cell flow path of each electrode portion 120 is formed. The directional end is in contact with the peripheral edge of one bottom surface 114 of the honeycomb structure 110, and the other end of the electrode portion 120 in the direction of the cell flow path is in contact with the peripheral edge of the other bottom surface 116 of the honeycomb structure 110. means.

In one embodiment of the electrically heated honeycomb structure according to the present invention, the energization resistance can be 100Ω or less. The energization resistance is obtained under the following measurement conditions. Terminals 130 are connected to the central portion in the extending direction of the cells of each electrode portion and to the central portion in the outer peripheral direction of the honeycomb structure portion (see FIG. 2). Next, after applying a voltage of 30 V between both terminals, the resistance value is obtained based on the current value after 30 seconds have elapsed. The energization resistance is preferably 100 Ω or less, more preferably 50 Ω or less, and can be, for example, 2 to 40 Ω.

(4-3 applications)
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. Further, 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 energizing and generating heat in the electrically heated honeycomb structure during heating for filter regeneration can be considered.

Hereinafter, examples for better understanding the present invention and its advantages will be illustrated, but the present invention is not limited to the examples.

<1. Manufacture of SiC fired body>
(SiC fired body 1)
74.5 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 25.5 g of carbon black powder with a specific surface area of 110 m ² / g, 7.8 g of Ni powder with a D50 of 35 μm, and water. Was prepared in an amount of 50 g. The mixed powder obtained by mixing these with a rotation / revolution stirrer was press-molded to prepare a cylindrical molded body having a diameter of 25 mm and a diameter of H15 mm. Next, the obtained molded product was dried at 100 ° C. and then fired at 1450 ° C. in an argon atmosphere for 2 hours to obtain a fired product.

(SiC fired body 2)
73.7 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 26.3 g of carbon black powder with a specific surface area of 110 m ² / g, 7.7 g of Ni powder with a D50 of 35 μm, and water. Was prepared in an amount of 50 g. The mixed powder obtained by mixing these with a rotation / revolution stirrer was press-molded to prepare a cylindrical molded body having a diameter of 25 mm and a diameter of H15 mm. Next, the obtained molded product was dried at 100 ° C. and then fired at 1450 ° C. in an argon atmosphere for 2 hours to obtain a fired product.

(SiC fired body 3)
74.5 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 25.5 g of carbon black powder with a specific surface area of 110 m ² / g, 4.7 g of Ni powder with a D50 of 35 μm, and methyl cellulose. 4 g and 50 g of water were prepared. The mixed powder obtained by mixing these with a rotation / revolution stirrer was extruded to prepare a prismatic molded body having a size of 25 mm × 5 mm × 50 mm. Next, the obtained molded product was dried at 100 ° C., degreased in an air atmosphere at 300 ° C. for 5 hours, and then calcined at 1450 ° C. in an argon atmosphere for 2 hours to obtain a calcined product.

(SiC fired body 4)
7.37 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 26.3 g of carbon black powder with a specific surface area of 110 m ² / g, 3.5 g of Al powder with a D50 of 13 μm, and methyl cellulose. 4 g and 50 g of water were prepared. The mixed powder obtained by mixing these with a rotation / revolution stirrer was extruded to prepare a prismatic molded body having a size of 25 mm × 5 mm × 50 mm. Next, the obtained molded product was dried at 100 ° C., degreased in an air atmosphere at 300 ° C. for 5 hours, and then calcined at 1450 ° C. in an argon atmosphere for 2 hours to obtain a calcined product.

(SiC fired body 5)
7.37 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 26.3 g of carbon black powder with a specific surface area of 110 m ² / g, 12.0 g of Zr powder with a D50 of 11 μm, and water. Was prepared in an amount of 50 g. The mixed powder obtained by mixing these with a rotation / revolution stirrer was press-molded to prepare a cylindrical molded body having a diameter of 25 mm and a diameter of H15 mm. Next, the obtained molded product was dried at 100 ° C. and then fired at 1450 ° C. in an argon atmosphere for 2 hours to obtain a fired product.

(SiC fired body 6)
7.37 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 26.3 g of carbon black powder with a specific surface area of 110 m ² / g, 8.3 g of Cu powder with a D50 of 28 μm, and water. Was prepared in an amount of 50 g. The mixed powder obtained by mixing these with a rotation / revolution stirrer was press-molded to prepare a cylindrical molded body having a diameter of 25 mm and a diameter of H15 mm. Next, the obtained molded product was dried at 100 ° C. and then fired at 1450 ° C. in an argon atmosphere for 2 hours to obtain a fired product.

(SiC fired body 7)
7.37 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 26.3 g of carbon black powder with a specific surface area of 110 m ² / g, 7.7 g of Co powder with a D50 of 5 μm, and water. Was prepared in an amount of 50 g. The mixed powder obtained by mixing these with a rotation / revolution stirrer was press-molded to prepare a cylindrical molded body having a diameter of 25 mm and a diameter of H15 mm. Next, the obtained molded product was dried at 100 ° C. and then fired at 1450 ° C. in an argon atmosphere for 2 hours to obtain a fired product.

(SiC fired body 8)
7.37 g of metallic silicon powder (density 2.33 g / cm ³ ) with a D50 of 79 μm, 26.3 g of carbon black powder with a specific surface area of 110 m ² / g, 6.3 g of Ti powder with a D50 of 20 μm, and water. Was prepared in an amount of 50 g. The mixed powder obtained by mixing these with a rotation / revolution stirrer was press-molded to prepare a cylindrical molded body having a diameter of 25 mm and a diameter of H15 mm. Next, the obtained molded product was dried at 100 ° C. and then fired at 1450 ° C. in an argon atmosphere for 2 hours to obtain a fired product.

Using each sample of the obtained SiC fired bodies 1 to 8, the porosity and the average pore diameter were measured using a porosimeter (Autopore IV9520 manufactured by Micromeritex Co., Ltd.). The results are shown in Table 1.

<2. Manufacture of SiC powder>
Examples and comparisons having the particle size distributions shown in Table 2 by selecting and pulverizing the obtained SiC fired bodies 1 to 8 according to the test numbers shown in Table 2 and then classifying them with an air classifier. An example SiC powder was obtained. The particle size distribution shown in Table 2 was determined based on the volume-based cumulative particle size distribution measured by a laser diffraction type particle size distribution measuring device of LA-950V2 manufactured by HORIBA.

When the types of SiC crystal phases were analyzed by X-ray diffraction (XRD) for each of the SiC powders of Examples and Comparative Examples, only β-SiC was detected. Further, for each of the SiC powders of Examples and Comparative Examples, the stacking defects (%) of β-SiC were determined according to the method described above. The results are shown in Table 2. Further, when the crystallite size of each of the SiC powders of Examples and Comparative Examples was determined according to the method described above, it was found to be 1000 Å or more.

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

<3. Manufacture of honeycomb structure>
(1) Preparation of Electrode Forming Paste 72 g of each SiC powder of 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 with a rotating and revolving stirrer to prepare an electrode portion-forming paste.

(2) Preparation of Dried Honeycomb Body A honeycomb molding raw material was prepared by mixing 6 kg of metallic silicon powder, 14 kg of SiC powder, 1 kg of cordierite powder, 1.6 kg of methyl cellulose, and 8 kg of water, and kneading with a kneader. Next, the obtained honeycomb molding raw material was vacuum-kneaded to obtain clay, and the obtained clay was extruded to obtain a columnar honeycomb molded body. The obtained honeycomb molded product was dried at 120 ° C. to obtain a honeycomb dried product.

(3) Preparation of Honeycomb Structure A pre-prepared electrode portion forming paste is applied to the side surface of the obtained honeycomb dried body to a thickness of 200 μm and dried at 80 ° C. to obtain a honeycomb dried body with an electrode forming slurry. It was. The specific coating conditions are as follows. The electrode portion-forming paste has a central angle defined by two line segments connecting both ends of each slurry and the central axis of the dried honeycomb when the dried honeycomb is observed in a cross section orthogonal to the flow path direction of the cell. The screen was printed in two places in a strip shape over the entire length between both bottom surfaces of the dried honeycomb so that the temperature was 50 °. Further, the electrode portion-forming pastes at the two locations were arranged so as to be on opposite sides of the central axis of the dried honeycomb body.

Next, the dried honeycomb structure with the electrode portion forming paste was degreased, fired, and oxidized to prepare an electrically heated honeycomb structure. Solventing was performed in the air at 450 ° C. for 5 hours. The firing was carried out for 2 hours in an argon atmosphere at 1450 ° C. The oxidation treatment was carried out in the air at 1000 ° C. for 5 hours.

The honeycomb structure portion 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 was 100 mm, and the length of the cell in the extending direction was 100 mm.

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

100 Electric heating type honeycomb structure 110 Honeycomb structure 112 Outer peripheral side wall 114 First bottom surface 116 Second bottom surface 118 Partition wall 120 Electrode part 122 Terminal connection part

Claims

Contains 70% by mass or more of β-SiC
A SiC powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in a volume-based cumulative particle size distribution measured by a laser diffraction method.
The SiC powder according to claim 1, wherein the integrated volume of particles having 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, wherein D50 is 15 to 35 μm and D10 is 7 to 20 μm in the volume-based cumulative particle size distribution measured by the laser diffraction method.
The SiC powder according to any one of claims 1 to 3, wherein 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 defect of β-SiC contained in the powder is 5% or less.
The SiC powder according to any one of claims 1 to 5, wherein the stacking defect of β-SiC contained in the powder is more than 2%.
The SiC powder according to any one of claims 1 to 6, further containing one or both of metallic silicon and metallic silicide.
The invention according to any one of claims 1 to 7, which contains one or more metal elements selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co and Zr. SiC powder.
The SiC powder according to claim 8, wherein the total concentration of the metal elements in the powder is 6% by mass or less.
A process of molding a mixture containing a SiC raw material powder and a metal powder to prepare a molded product, and
A step of firing the molded product at a temperature of 1800 ° C. or lower in an inert atmosphere to obtain a fired product containing β-SiC.
A step of crushing the fired body to obtain a crushed fired body, and
A step of classifying the crushed fired body to obtain a powder having a D50 of 8 to 35 μm and a D10 of 5 μm or more in the volume-based cumulative particle size distribution measured by a laser diffraction method.
A method for producing a SiC powder containing.
The method for producing SiC powder according to claim 10, wherein the powder has an integrated volume of 7% or less 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.
The method for producing a SiC powder according to claim 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.
The method for producing an SiC powder according to any one of claims 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.
The metal powder is any one of claims 10 to 13 containing one or more metal particles selected from the group consisting of Ni, Al, B, N, Ga, Ge, Ti, Cu, Co and Zr. The method for producing SiC powder according to item 1.
The method for producing SiC powder according to any one of claims 10 to 14, wherein the fired body has a porosity of 35 to 80%.
The method for producing SiC powder according to any one of claims 10 to 15, wherein the average pore diameter of the fired body is 5 to 300 μm.
By forming and drying the clay, the outer peripheral side wall and a plurality of cells which are arranged on the inner peripheral side of the outer peripheral side wall and extend from the first bottom surface to the second bottom surface to serve as a fluid flow path are formed. The process of obtaining a columnar honeycomb molded body having a partition wall,
The electrode portion forming paste is applied to the first region and the second region of the side surface of the honeycomb molded product or the honeycomb molded product obtained by firing, respectively, and the electrode portion is formed. A step of forming an electrode portion by drying and firing the paste to form a pair of electrode portions is provided.
One or both of the clay and the electrode portion-forming paste contains 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 obtained by the manufacturing method according to claim 17.
An electrically heated honeycomb structure containing the SiC powder according to any one of claims 1 to 9.