Ceramic body and electric heating element

Abstract

The present invention provides a ceramic body that can be used in electric heaters capable of continuously generating heat for extended periods in high-temperature environments. [Solution] The ceramic body contains a plurality of ceramic particles 1, each containing one or more elements selected from silicon carbide, silicon nitride, and aluminum nitride; a silicon phase 2, where a dopant is dissolved, existing between the plurality of ceramic particles 1; and a plurality of dopant particles 3, which are present in the silicon phase 2 and contain a dopant. The dopant is a group 13 or group 15 element. The silicon phase 2 content in the ceramic body is 20-80% by mass. The porosity of the ceramic body is 30% or less.

Description

[Technical Field]

[0001] This invention relates to a ceramic body and an electric heating heater. [Background technology]

[0002] Industrial heaters are used to heat objects in various products and production equipment, and one type known is the electric heating heater using a honeycomb structure. In an electric heating heater, electrodes are arranged on a honeycomb structure made of conductive ceramics, and the honeycomb structure can be heated by applying an electric current.

[0003] For example, Patent Document 1 proposes a honeycomb structure in which particles containing one or more elements selected from silicon carbide, silicon nitride, and aluminum nitride, and silicon doped with a dopant, wherein the dopant is a group 13 or group 15 element, the silicon content is 20-80% by mass, and the porosity is 30% or less. Because this honeycomb structure controls the amount of silicon dopant, it can suppress the generation of excess current. Furthermore, Patent Document 2 proposes a honeycomb structure in which the partition walls and outer periphery walls are composed of ceramics containing silicon carbide and silicon, and an oxide film with a thickness of 0.1 μm to 5.0 μm is formed on the silicon surface. Because this honeycomb structure has a predetermined oxide film, it has an excellent balance between oxidation resistance and thermal shock resistance. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-142543 [Patent Document 2] Japanese Patent Publication No. 2022-145495 [Overview of the project] [Problems that the invention aims to solve]

[0005] The honeycomb structures described in Patent Documents 1 and 2 are primarily used as catalyst supports for purifying automobile exhaust gases and are not suitable for other applications. In particular, various industrial heaters are sometimes required to continue generating heat in high-temperature environments (e.g., 600-1200°C), but the honeycomb structures described in Patent Documents 1 and 2 have difficulty continuing to generate heat in high-temperature environments.

[0006] This invention was made to solve the above-mentioned problems, and aims to provide a ceramic body that can be used in an electric heating heater that can continue to generate heat for a long period of time in a high-temperature environment. Furthermore, the present invention aims to provide an electric heating heater that can continue to generate heat for a long period of time in a high-temperature environment. [Means for solving the problem]

[0007] For an electric heater to continue generating heat for a long period of time in a high-temperature environment, it is necessary to suppress the increase in resistance of the ceramic body used in the electric heater in such a high-temperature environment. The inventors of this invention have diligently researched ceramic bodies and have found that the reason why the resistance of ceramic bodies increases in a high-temperature environment is that the amount of dopant dissolved in the silicon phase decreases in such a high-temperature environment. Therefore, the inventors of this invention have found that by leaving dopants as a solid phase (dopant particles) in the silicon phase present between the ceramic particles, even if the amount of dopant dissolved in the silicon phase decreases in a high-temperature environment, the dopant in the dopant particles can remain dissolved in the silicon phase, maintaining the amount of dopant in the silicon phase, and thus suppressing the increase in resistance, thus completing the present invention. That is, the present invention is illustrated as follows.

[0008] <1> Multiple ceramic particles comprising one or more selected from silicon carbide, silicon nitride, and aluminum nitride, A silicon phase in which the dopant is solid-dissolved exists between a plurality of the aforementioned ceramic particles, A plurality of dopant particles that are present in the silicon phase and contain a dopant, and A ceramic body containing, The dopant is a Group 13 element or a Group 15 element, The content of the silicon phase in the ceramic body is 20 to 80% by mass, The ceramic body having a porosity of 30% or less.

[0009] <2> The ceramic body according to <1>, wherein the silicon phase exists as a continuous phase.

[0010] <3> The ceramic body according to <1> or <2>, wherein the content of the dopant in the dopant particles in the ceramic body is 0.001% by mass or more.

[0011] <4> The ceramic body according to any one of <1> to <3>, wherein a silicon oxide film is formed on at least a part of the surface and / or inside of the ceramic body, and the content of the silicon oxide film in the ceramic body is 0.1% by mass or more.

[0012] <5> The concentration of the dopant dissolved in the silicon phase is 1×10 16 ~5×10 20 per cm 3 The ceramic body according to any one of <1> to <4>.

[0013] <6> The ceramic body according to any one of <1> to <5>, which is a honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and partitioning a plurality of cells extending from a first end face to a second end face.

[0014] <7> The ceramic body according to any one of <1> to <6>, which is used for an electric heating heater.

[0015] <8> An electric heating heater including the ceramic body according to any one of <1> to <7>.

[0016] <9> The electric heating heater according to <8>, further comprising a pair of electrode portions provided on the ceramic body and electrode terminals connected to the pair of electrode portions.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a ceramic body that can be used for an electric heating heater that can continue to generate heat for a long time in a high-temperature environment. Moreover, according to the present invention, it is possible to provide an electric heating heater that can continue to generate heat for a long time in a high-temperature environment.

Brief Description of the Drawings

[0018] [Figure 1] It is a partial schematic cross-sectional view of a ceramic body according to an embodiment of the present invention. [Figure 2] It is a perspective view of an electric heating heater according to an embodiment of the present invention. [Figure 3] It is a front view of a surface orthogonal to the direction in which cells of another electric heating heater according to an embodiment of the present invention extend.

Modes for Carrying Out the Invention

[0019] The ceramic body of the present invention contains a plurality of ceramic particles, one or more selected from silicon carbide, silicon nitride, and aluminum nitride; a silicon phase present between the plurality of ceramic particles in which dopants are solid-dissolved; and a plurality of dopant particles present in the silicon phase and containing dopants. The dopants are group 13 or group 15 elements. The silicon phase content in the ceramic body is 20 to 80% by mass. The porosity of the ceramic body is 30% or less. By having the above configuration, even if the amount of dopants solid-dissolved in the silicon phase decreases in a high-temperature environment, the dopants in the dopant particles can solid-dissolve in the silicon phase to maintain the amount of dopants in the silicon phase (especially, maintain it at the solid-solution limit). As a result, the increase in resistance of the ceramic body in a high-temperature environment can be suppressed, and when used in an electric heating heater, it can continue to generate heat for a long period of time in a high-temperature environment.

[0020] The embodiments of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that modifications, improvements, etc., to the following embodiments, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention, also fall within the scope of the present invention.

[0021] Figure 1 is a partial schematic cross-sectional view of a ceramic body according to an embodiment of the present invention. As shown in Figure 1, the ceramic body according to an embodiment of the present invention contains ceramic particles 1, a silicon phase 2, and dopant particles 3. Note that Figure 1 illustrates the case where the porosity of the ceramic body is 0% (no pores), but pores may be present.

[0022] The ceramic particles 1 contain one or more selected from silicon carbide, silicon nitride, and aluminum nitride. These ceramic particles 1 function as aggregate particles in the ceramic body, thereby strengthening it. In particular, it is preferable that the main component of the ceramic particles 1 is silicon carbide, as this results in higher thermal conductivity and a smaller difference in thermal expansion coefficients with the silicon phase 2. Note that the main component of the ceramic particles 1 being silicon carbide means that the proportion of silicon carbide in the ceramic particles 1 is 80% by mass or more, preferably 90% by mass or more. The proportion of each component in ceramic particle 1 is determined by observing the cross-section of the ceramic body to identify the ceramic particle 1 and measuring the amount of each component contained in the ceramic particle 1 using X-ray fluorescence.

[0023] Silicon phase 2 exists between multiple ceramic particles 1, and the dopant is dissolved in it. By dissolving the dopant in silicon phase 2, the volume resistivity of the ceramic body can be effectively reduced. The silicon phase 2 content in the ceramic body is 20 to 80% by mass. By setting the silicon phase 2 content to 20% by mass or more, the volume resistivity of the ceramic body is reduced, which effectively suppresses the generation of excess current. Furthermore, a good balance is achieved between the strength and Young's modulus of the ceramic body, thereby improving thermal shock resistance. In addition, by setting the silicon phase 2 content to 80% by mass or less, the shape stability of the ceramic body can be improved. From the viewpoint of stably ensuring the above effects, the silicon phase 2 content in the ceramic body is preferably 30 to 80% by mass, and more preferably 40 to 80% by mass. The silicon phase 2 content in a ceramic body is determined as follows. First, the amount of silicon is measured in a cross-section of the ceramic body using the X-ray fluorescence method. At this time, the amount of silicon measured includes not only the amount of silicon in silicon phase 2 but also the amount of silicon contained in ceramic particles 1 (such as silicon carbide or silicon nitride). Therefore, the amount of silicon phase 2 is obtained by subtracting the amount of silicon in ceramic particles 1 measured above from the amount of silicon measured. If a silicon oxide film, as described later, is formed on the surface and / or in at least a part of the interior of the ceramic body, the amount of silicon measured by the X-ray fluorescence method also includes the amount of silicon contained in the silicon oxide film. Therefore, the amount of silicon is calculated from the content of the silicon oxide film measured by the method described later, and the amount of silicon phase 2 is obtained by further subtracting this amount of silicon.

[0024] In ceramic materials, it is preferable that silicon phase 2 exists as a continuous phase. If silicon phase 2 is a continuous phase, it becomes easier to control the volume resistivity of the ceramic material to a low level. Here, the existence of silicon phase 2 as a continuous phase means that it is a matrix-domain structure in which silicon phase 2 is the matrix and ceramic particles 1 are the domains.

[0025] The dopant dissolved in silicon phase 2 is a group 13 or group 15 element. Here, Group 13 elements refer to boron (B), aluminum (Al), gallium (Ga), indium (In), etc., and Group 15 elements refer to nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), etc. Dopants dissolved in silicon phase 2 can exhibit conductivity without being affected by counter-doping as long as they are elements of the same group, so they may contain multiple types of elements. Preferably, the dopant is one or two selected from B and Al, or one or two selected from N and P.

[0026] The concentration of the dopant dissolved in silicon phase 2 is not particularly limited and can be adjusted appropriately according to the required volume resistivity of the ceramic body, but is preferably 1 × 10⁻⁶ 16 ~5×1020 pieces / cm 3 、 more preferably 5×10 17 ~5×10 20 pieces / cm 3 is. By controlling the concentration of the dopant within this range, it becomes easier to reduce the volume resistivity of the ceramic body. Generally, as the concentration of the dopant dissolved in the silicon phase 2 increases, the volume resistivity of the ceramic body decreases, and as the concentration of the dopant dissolved in the silicon phase 2 decreases, the volume resistivity of the ceramic body tends to increase.

[0027] Regarding the concentration of the dopant dissolved in the silicon phase 2, it can be determined in accordance with the silicon separation ICP emission spectrometry specified in JIS G1322-3:2010 "Methods for Analysis of Metallic Silicon". Specifically, the ceramic body is decomposed with nitric acid and hydrofluoric acid, perchloric acid is added, heated to generate white smoke of perchloric acid, silicon is volatilized and separated as silicon tetrafluoride, and then the salts are dissolved in water. Next, the boron contained in the solution is measured by ICP emission spectrometry, and the boron concentration in silicon is calculated. This calculated boron concentration is taken as the concentration of boron dissolved in the silicon phase 2. Note that other dopants other than boron can also be measured by the same method.

[0028] The dopant particles 3 are present in the silicon phase 2 and contain a dopant. The dopant is of the same type as the dopant dissolved in the silicon phase 2. Therefore, the dopant contained in the dopant particles 3 is a Group 13 element or a Group 15 element. By causing the dopant particles 3 to be present in the silicon phase 2, even when the amount of the dopant dissolved in the silicon phase 2 decreases in a high-temperature environment, the dopant in the dopant particles 3 can dissolve in the silicon phase 2 to maintain (especially, maintain at the solid solubility limit) the amount of the dopant in the silicon phase. As a result, an increase in resistance of the ceramic body in a high-temperature environment can be suppressed, and when used in an electric heating heater, it becomes possible to continuously generate heat for a long time in a high-temperature environment.

[0029] Dopant particles 3 can be present in silicon phase 2 in the form of various compounds. Specifically, they can be present in silicon phase 2 as compounds such as carbides, nitrides, and borides. Examples of compounds include B4C, TiB2, BN, AlN, GaN, InN, and Al4C3.

[0030] The dopant content in the dopant particles 3 in the ceramic body is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and even more preferably 0.003% by mass or more. By controlling the dopant content in the dopant particles 3 in the ceramic body within this range, the effect of maintaining the amount of dopant in the silicon phase (especially maintaining it at the solid solubility limit) by solid dissolving the dopant in the dopant particles 3 in the silicon phase 2 under high-temperature conditions can be stably ensured. The higher the dopant content in dopant particles 3 in the ceramic body, the easier it is to obtain the above effects. Therefore, there is no particular upper limit, but for example, it is 5,000% by mass or less, 4,000% by mass or less, or 3,000% by mass or less. With a dopant content in dopant particles 3 in the ceramic body within this range, the properties of the ceramic body, such as strength, are less likely to deteriorate.

[0031] The dopant content in dopant particles 3 in a ceramic body can be measured by the following method. First, a total of five samples are taken from the ceramic body near the center in both the height and radial directions. Each sample should be 1 cm in size. 3 The sample is cubic in size (1cm x 1cm x 1cm). After observing the sample at a magnification of 1000x using SEM (Scanning Electron Microscope) to identify dopant particle 3, dopant particle 3 is analyzed by SIMS (Secondary Ion Mass Spectrometry) to determine the dopant content in dopant particle 3 within the ceramic body. The average value of the content in five samples is used as the result for the dopant content in dopant particle 3 within the ceramic body.

[0032] The porosity of the ceramic material is 30% or less. By reducing the porosity of the ceramic material to 30% or less, the thermal conductivity of the ceramic material is improved, and thus the thermal shock resistance is also increased. From the viewpoint of stably ensuring this effect, the porosity of the ceramic material is preferably 20% or less, more preferably 10% or less. The lower limit of the porosity of the ceramic material is not particularly limited and may be 0% (no pores). The porosity of the ceramic material was measured using a mercury porosimeter.

[0033] It is preferable that a silicon oxide film is formed on the surface and / or on at least a portion of the interior of the ceramic body. Furthermore, it is preferable that the silicon oxide film content in the ceramic body is 0.1% by mass or more. By forming a silicon oxide film on the surface and / or on at least a portion of the interior of the ceramic body, the balance between oxidation resistance and thermal shock resistance of the ceramic body in high-temperature environments can be improved. From the viewpoint of stably ensuring this effect, the silicon oxide film content in the ceramic body is preferably 0.2% by mass or more, more preferably 0.3% by mass or more. The upper limit of the silicon oxide film content in the ceramic body is not particularly limited, but for example, it is 5.0% by mass, 4.0% by mass, or 3.0% by mass. Here, the surface of a ceramic body on which a silicon oxide film can be formed refers to the surface of a ceramic body where silicon is exposed. Furthermore, the interior of a ceramic body on which a silicon oxide film can be formed refers to the pore surface of the ceramic body where silicon is exposed.

[0034] The silicon oxide film content in ceramic materials can be calculated by assuming that the amount of oxygen elements measured by inert gas fusion infrared absorption spectroscopy is entirely attributable to the silicon oxide film, and then calculating the molecular weight.

[0035] The shape of the ceramic body is not particularly limited and can be appropriately adjusted according to the application of the electric heating heater used. For example, the shape of the ceramic body can be a honeycomb structure. A ceramic body having a honeycomb structure (hereinafter referred to as the "honeycomb structure") may have an outer periphery wall and partition walls disposed inside the outer periphery wall, which divide and form a plurality of cells extending from a first end face to a second end face. By using a honeycomb structure, the fluid flowing through the cells can be easily heated.

[0036] The ceramic body can be manufactured according to known methods. For example, the ceramic body can be manufactured according to the method described below. For example, first, a molding raw material is prepared by adding a binder, surfactant, water, etc., to a ceramic powder containing ceramic particles 1 and dopant particles 3.

[0037] Examples of binders include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxylcellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Among these, it is preferable to use methylcellulose and hydroxypropoxylcellulose in combination. The binder content is preferably 2.0 to 10.0 parts by mass when the mass of the ceramic powder is 100 parts by mass.

[0038] The water content is preferably 20 to 60 parts by mass when the mass of the ceramic powder is 100 parts by mass.

[0039] As surfactants, ethylene glycol, dextrin, fatty acid soap, polyalcohol, etc., can be used. These may be used individually or in combination of two or more. The surfactant content is preferably 0.1 to 2.0 parts by mass when the mass of the ceramic powder is 100 parts by mass.

[0040] Pore-forming materials may be added to the molding raw material as needed. Examples of pore-forming materials include starch, foamed resin, and water-absorbent resin.

[0041] Next, the obtained molding raw material is kneaded to form a clay base, which is then molded to produce a ceramic molded body. In particular, when producing a honeycomb structured ceramic molded body (hereinafter referred to as "honeycomb molded body"), the clay base is extruded to produce a raw (unfired) honeycomb molded body. In extrusion molding, a die having the desired overall shape, cell shape, partition wall thickness, cell density, etc., can be used.

[0042] Next, the obtained ceramic molded body (honeycomb molded body) is dried and degreased to produce a degreased ceramic body (honeycomb degreased body). The degreasing process is carried out at 300-500°C in an air atmosphere, an inert atmosphere, or a reduced-pressure atmosphere. After that, the degreased ceramic body (honeycomb degreased body) is impregnated with silicon (metallic silicon) containing a solid-solution dopant in a reduced-pressure inert gas or vacuum and fired. Through this impregnation firing, the pores in the degreased ceramic body (honeycomb degreased body) are filled with molten silicon and solidified, making it possible to reduce the porosity of the ceramic body (honeycomb structure) to 30% or less. Examples of inert atmospheres include a nitrogen gas atmosphere, a noble gas atmosphere such as argon, or a mixed gas atmosphere. As a method for impregnating and firing the silicon containing a solid-solution dopant, one method is to arrange the mass containing the silicon containing the solid-solution dopant and the degreased ceramic body (honeycomb degreased body) in contact and then fire them.

[0043] The firing temperature is preferably 1350°C or higher, more preferably 1400°C or higher, and even more preferably 1450°C or higher, in order to ensure sufficient sintering. Furthermore, the firing temperature is preferably 2200°C or lower, more preferably 1800°C or lower, and even more preferably 1600°C or lower, in order to reduce manufacturing costs during firing.

[0044] To ensure sufficient sintering, the heating time for the degreased ceramic body (honeycomb degreased body) at the above firing temperature is preferably 0.25 hours or more, more preferably 0.5 hours or more, and even more preferably 0.75 hours or more. Furthermore, to reduce manufacturing costs during firing, the heating time for the degreased ceramic body (honeycomb degreased body) at the above firing temperature is preferably 5 hours or less, more preferably 4 hours or less, and even more preferably 3 hours or less.

[0045] Furthermore, after impregnation and firing, it is preferable to perform an oxidation treatment at 1000 to 1350°C for 1 to 300 hours to improve durability. Oxidation treatment refers to heat treatment in an oxidizing atmosphere (for example, under atmospheric pressure). By performing such heat treatment, a silicon oxide film can be formed on the surface and / or in part of the interior of the ceramic body (honeycomb structure).

[0046] The ceramic body according to the embodiment of the present invention can generate heat by Joule heating when an electric current is passed through it. Furthermore, even if the amount of dopant dissolved in the silicon phase 2 decreases in a high-temperature environment, the dopant in the dopant particles 3 can remain dissolved in the silicon phase 2, maintaining the amount of dopant in the silicon phase (especially maintaining it at the solid solubility limit). For this reason, the ceramic body according to the embodiment of the present invention can be used in an electric heating heater, enabling the electric heating heater to continue generating heat for a long period of time in a high-temperature environment.

[0047] An electric heating heater according to an embodiment of the present invention comprises the above-described ceramic body. An example of this electric heating heater is shown in Figure 2. Figure 2 is a perspective view of an electric heating heater according to an embodiment of the present invention. The electric heating heater shown in Figure 2 comprises a ceramic body having a honeycomb structure (hereinafter referred to as the "honeycomb structure part 10"), a pair of electrode parts 20, a slit 30, and a filler material 40. The honeycomb structure 10 has an outer periphery wall 11 and partition walls 15 disposed inside the outer periphery wall 11, which divide and form a plurality of cells 14 extending from a first end face 12 to a second end face 13. The plurality of cells 14 serve as fluid flow paths. A pair of electrode portions 20 are disposed on the outer periphery wall 11. One or more slits 30 are provided in the honeycomb structure 10. At least a portion of the space of the slit 30 is filled with a filler material 40. In Figure 1, an example is shown in which the entire space of the slit 30 is filled with the filler material 40, but the filler material 40 may be filled only in a portion of the space of the slit 30. A honeycomb structure having the above-described structure can generate heat in the honeycomb structure 10 by Joule heating when an electric current is passed from a pair of electrode parts 20 to the honeycomb structure 10.

[0048] If the main component of the honeycomb structure 10 is silicon carbide or a silicon-silicon carbide composite, the filler 40 preferably contains 20% by mass or more of silicon carbide, and more preferably 20 to 70% by mass. This makes it possible to set the thermal expansion coefficient of the filler 40 to a value close to that of the honeycomb structure 10, thereby improving the thermal shock resistance of the honeycomb structure 10. The filler 40 may also contain 30% by mass or more of silica, alumina, etc. The Young's modulus of the filler 40 is preferably 500 kPa or more and 1500 MPa or less. By keeping it within this range, stress can be efficiently buffered in the slit 30 during thermal shock, and the mechanical strength of the slit 30 can be maintained, suppressing chipping and cracking during manufacturing and use. From the viewpoint of stably ensuring this effect, the Young's modulus of the filler 40 is more preferably 10 to 1000 MPa.

[0049] The honeycomb structure 10 has a columnar shape and thickness in the direction in which the cells 14 extend. The ratio (aspect ratio) of the length of the cells 14 in the direction in which the honeycomb structure 10 extends to the width or diameter of each end face (first end face 12, second end face 13) is not particularly limited. Furthermore, the columnar shape may include a shape (flattened shape) in which the length of the cells 14 in the direction in which the honeycomb structure 10 extends is shorter than the width or diameter of each end face (first end face 12, second end face 13).

[0050] The external shape of the honeycomb structure 10 is not particularly limited, and can be other shapes such as a columnar shape with circular end faces (cylindrical), a columnar shape with oval end faces, or a columnar shape with polygonal end faces (square, pentagon, hexagon, heptagon, octagon, etc.). Note that the external shape of the honeycomb structure 10 in Figure 2 shows a columnar shape with square (rectangular) end faces as an example. Furthermore, the size of the honeycomb structure 10 is such that the area of ​​each end face is 2000 to 65000 mm², in order to improve heat resistance (suppress cracks in the circumferential direction of the outer wall 11). 2 Preferably, it is 5000 to 25000 mm 2 It is preferable that it be so.

[0051] The shape of the cell 14 on a plane perpendicular to the direction in which the cell 14 extends (the end face or cross-section of the honeycomb structure 10) is not particularly limited, but examples include a square, hexagon, octagon, or a combination thereof. Among these, the shape of the cell 14 is preferably a square or hexagon. With such a cell 14 shape, the pressure loss when a fluid such as exhaust gas flows through the honeycomb structure 10 can be reduced.

[0052] The thickness of the outer peripheral wall 11 is not particularly limited, but from the viewpoint of ensuring the structural strength of the honeycomb structure 10 and suppressing leakage of the fluid flowing through the cell 14 from the outer peripheral wall 11, it is preferably 0.05 mm or more, more preferably 0.10 mm or more, and even more preferably 0.15 mm or more. However, if the outer peripheral wall 11 is made too thick, it will become too strong, disrupting the strength balance with the partition wall 15 and potentially reducing thermal shock resistance. For this reason, the thickness of the outer peripheral wall 11 is preferably 4.0 mm or less, more preferably 3.0 mm or less, and even more preferably 2.0 mm or less. The thickness of the outer perimeter wall 11 refers to the thickness in the direction normal to the tangent of the outer perimeter wall 11 at the measurement point, when the location of the outer perimeter wall 11 to be measured is observed on a plane perpendicular to the direction in which the cell 14 extends.

[0053] The thickness of the partition wall 15 is not particularly limited, but is preferably 0.05 to 0.8 mm, and more preferably 0.1 to 0.6 mm. By making the thickness of the partition wall 15 0.05 mm or more, it is possible to suppress a decrease in the strength of the honeycomb structure 10. By making the thickness of the partition wall 15 0.8 mm or less, it is possible to suppress an increase in pressure loss when exhaust gas is passed through, such as when the honeycomb structure 10 is used as a catalyst carrier. In this specification, the thickness of the partition wall 15 means the length of the portion of the line segment that passes through the partition wall 15, which connects the centroids of adjacent cells 14 in a plane perpendicular to the direction in which the cells 14 extend.

[0054] The cell density of the honeycomb structure 10 is not particularly limited, but is preferably 4 to 150 cells / cm². 2 Comfortably 7-100 cells / cm 2 By controlling the cell density within this range, pressure loss can be reduced when fluids such as exhaust gas flow through it. In this specification, cell density refers to the value obtained by dividing the number of cells by the area of ​​one end face of the honeycomb structure 10 excluding the outer periphery wall 11.

[0055] The slit 30 provided in the honeycomb structure 10 is formed by removing or eliminating the outer peripheral wall 11 and / or partition wall 15. The slit 30 may extend from the first end face 12 to the second end face 13 of the honeycomb structure 10.

[0056] The pair of electrode portions 20 are formed from a conductive material. The conductive material used for the pair of electrode portions 20 is not particularly limited, but it is preferably an oxide ceramic or a mixture of a metal or metal compound and an oxide ceramic. The metal may be either a single metal or an alloy, and for example, silicon, aluminum, iron, stainless steel, titanium, tungsten, Ni-Cr alloy, etc. can be suitably used. The metal compound may be anything other than an oxide ceramic, such as a metal oxide, metal nitride, metal carbide, metal silicide, metal boride, or composite oxide, and for example, FeSi2, CrSi2, alumina, silica, titanium oxide, etc. can be suitably used. The metal and metal compound may be a single type or two or more types may be used in combination. Specific examples of oxide ceramics include glass, cordierite, and mullite. The glass may further contain an oxide consisting of at least one component selected from the group consisting of B, Mg, Al, Si, P, Ti, and Zr.

[0057] The thickness of the pair of electrode portions 20 is not particularly limited, but is preferably 0.01 to 5 mm, more preferably 0.01 to 3 mm. By controlling it within this range, the honeycomb structure can be heated uniformly. If the thickness of the pair of electrode portions 20 is 0.01 mm or more, the electrical resistance is appropriately controlled, and heating can be achieved more uniformly. If the thickness of the pair of electrode portions 20 is 5 mm or less, the risk of damage is reduced. In this specification, the thickness of the pair of electrode portions 20 refers to the thickness of the outer surface of the pair of electrode portions 20 in the direction normal to the tangent at the measurement location, when the location of the pair of electrode portions 20 whose thickness is to be measured is observed in a plane perpendicular to the direction in which the cell 14 extends.

[0058] The electrical resistivity of the pair of electrode portions 20 is not particularly limited, but is preferably 1 × 10⁻⁶. -7 ~5×10 -1 Ω·m, more comfortable 5×10 -7 ~2.5×10 -1 Ω·m, more preferably 1 × 10 -6 ~1.25×10-1 It is Ω·m. In particular, the electrical resistivity of the pair of electrode parts 20 is 5 × 10 -1 By setting the resistance to Ω·m or less, the resistance during electrical heating can be reduced. In this specification, the electrical resistivity of the pair of electrode portions 20 refers to the value measured at 400°C using the four-terminal method.

[0059] The position of the pair of electrode portions 20 is not particularly limited as long as it is on the outer peripheral wall 11 of the honeycomb structure portion 10. Similarly, the position of the slit 30 provided in the honeycomb structure portion 10 is not particularly limited. For example, in one embodiment, as shown in Figure 2, the honeycomb structure has a pair of electrode portions 20 arranged on one plane of the outer peripheral wall 11 of the rectangular prism-shaped honeycomb structure portion 10, and the slit 30 may include a first slit 31 extending inward from the outer peripheral wall 11 between the pair of electrode portions 20. By controlling the positions of the pair of electrode portions 20 and the first slit 31 in this way, the heat distribution of the honeycomb structure can be adjusted.

[0060] As shown in Figure 2, the slit 30 may further include a second slit 32 extending inward from two outer peripheral walls 11 perpendicular to the outer peripheral wall 11 on which a pair of electrode portions 20 are provided, and a third slit 33 that intersects with the first slit 31 and does not reach the outer peripheral wall 11. In this case, it is preferable that the second slit 32 and the third slit 33 are arranged alternately. With this configuration, the current flows while bypassing along the second slit 32 and the third slit 33 as indicated by the arrows in the honeycomb structure portion 10 shown in Figure 2, making it easier to heat the honeycomb structure uniformly.

[0061] Furthermore, the honeycomb structure may have multiple honeycomb structural parts 10, and the multiple honeycomb structural parts 10 may be connected by conductive connectors 50. Figure 3 shows a front view of an electric heating heater having such a structure, from a plane perpendicular to the direction in which the cell extends. The electric heater shown in Figure 2 has a first honeycomb structure 10A and a second honeycomb structure 10B, and the first honeycomb structure 10A and the second honeycomb structure 10B are connected by a conductive connector 50. Even with this structure, the current flows while bypassing along the second slit 32 and the third slit 33 of the first honeycomb structure 10A and the second honeycomb structure 10B, making it easier to heat the electric heater uniformly.

[0062] Two conductive connectors 50 are provided on the outer peripheral wall 11 where the first honeycomb structure 10A and the second honeycomb structure 10B face each other. Specifically, the two conductive connectors 50 are each partially provided on the outer peripheral wall 11 at a position perpendicular to the first slit 31 and without straddling the first slit 31.

[0063] Various materials can be used for the conductive connector 50, but for example, Si-SiC composite materials, Si metal-impregnated Si-SiC composite materials, etc., may be used.

[0064] Electrode terminals (not shown) may be connected to the pair of electrode sections 20 as needed. The shape of the electrode terminals is arbitrary, but they may be columnar. By applying a voltage to the honeycomb structure through the electrode terminals, the honeycomb structure can be easily heated by Joule heating. The applied voltage is preferably 12 to 900V, and more preferably 48 to 600V, but the applied voltage can be changed as appropriate.

[0065] The electrode terminals can be made of ceramics or carbon. If the electrode terminals are made of ceramics, electrical connection to the honeycomb structure becomes possible. Alternatively, metal terminals may be joined to the tips of the electrode terminals. The joining of ceramic or carbon electrode terminals to metal terminals can be done by crimping, welding, conductive adhesive, etc. The metal terminals can be made of conductive metals such as iron alloys or nickel alloys.

[0066] The ceramics constituting the electrode terminals are not particularly limited, but examples include silicon carbide (SiC); metallic compounds such as tantalum silicide (TaSi2) and chromium silicide (CrSi2); and composite materials (cermets) containing one or more metals. Specific examples of cermets include composite materials of metallic silicon and silicon carbide, composite materials of metallic silicon and silicon carbide with metallic silicides such as tantalum silicide and chromium silicide, and composite materials in which one or more insulating ceramics such as alumina, mullite, zirconia, cordierite, silicon nitride, and aluminum nitride are added to one or more of the above metals from the viewpoint of reducing thermal expansion. It is preferable that the carbon constituting the electrode terminals is mainly composed of carbon. Mainly composed of carbon means that the carbon content is 50% by mass or more of the total components constituting the electrode terminals. More preferably, the carbon content is 80% by mass or more, and even more preferably 90% by mass or more.

[0067] Furthermore, a catalyst may be supported on the outer peripheral wall 11 facing the partition wall 15 or cell 14 of the honeycomb structure 10, as needed. Various catalysts can be used, but examples include a three-way catalyst and / or nickel oxide. By supporting the catalyst, purification performance can be obtained when exhaust gas or the like is flowed into the cell 14 as a fluid.

[0068] The method for manufacturing an electric heating heater according to the embodiment of the present invention is not particularly limited as long as a honeycomb structure having the above-described features can be manufactured. An example of a method for manufacturing an electric heating heater according to the embodiment of the present invention will be described below. A method for manufacturing a honeycomb structure according to an embodiment of the present invention comprises the steps of: S1 for obtaining a honeycomb molded body with electrode material attached; S2 for forming slits; S3 for firing the honeycomb molded body; and S4 for filling with filler material.

[0069] Step S1 is a step in which an electrode-forming raw material is applied to a honeycomb molded body, which is a precursor of the honeycomb structure 10, to obtain a honeycomb molded body with electrode-forming raw material. Here, the honeycomb molded body is the honeycomb structure 10 before firing, which is used to produce the honeycomb structure 10 described above, and can be manufactured by the method described above.

[0070] Next, electrode-forming raw materials for forming a pair of electrode portions 20 are prepared. When the main components of the pair of electrode portions 20 are silicon carbide and silicon, it is preferable to prepare the electrode-forming raw materials by adding predetermined additives to silicon carbide powder and silicon powder and kneading them together. Next, the obtained electrode-forming raw materials are applied to predetermined positions on the outer peripheral wall 11 of the dried honeycomb molded body (honeycomb dried body) to obtain a honeycomb molded body with electrode-forming raw materials. The method for preparing the electrode-forming raw materials and the method for applying the electrode-forming raw materials to the honeycomb molded body can be carried out in accordance with known methods for manufacturing honeycomb structures.

[0071] Alternatively, in the S1 step, the honeycomb molded body may be fired before applying the electrode-forming material. In other words, in the alternative manufacturing method, the honeycomb molded body is fired to produce a honeycomb-fired body, and the electrode-forming material is applied to the honeycomb-fired body to obtain a honeycomb-fired body with electrode-forming material instead of a honeycomb molded body with electrode-forming material.

[0072] Step S2 is a step in which slits are formed at predetermined positions in the honeycomb molded body with electrode material attached. It is preferable to form the slits using a rotary tool or the like. The slits are formed so as to open at predetermined positions in the honeycomb molded body with electrode material attached.

[0073] Step S3 is a process of firing the honeycomb molded body with electrode material attached to obtain a fired honeycomb body. Before firing, the honeycomb molded body with electrode material attached may be dried. Alternatively, pre-firing may be performed before firing to remove binders and other substances from the filler material. Preferably, the firing conditions are heating at 1400 to 1500°C for 1 to 20 hours in an inert atmosphere such as nitrogen or argon. After firing, it is preferable to perform oxidation treatment at 1200 to 1350°C for 1 to 300 hours to improve durability. The pre-firing and firing methods are not particularly limited and can be performed using an electric furnace, gas furnace, etc.

[0074] Furthermore, in step S3, the honeycomb molded body with electrode material attached may be heat-treated at 300 to 1500°C. This heat treatment may be included in the calcination and firing processes described above, or it may be performed separately from the calcination and firing processes.

[0075] Step S4 is the process of filling the slits formed in the honeycomb-fired body with filler material. In step S4, first, the filler material is prepared. The filler material is the raw material for producing the filler described above. For example, the insulating material can be obtained by kneading a mixture obtained by mixing the filler described above with a binder, surfactant, pore-forming agent, water, etc. The filler material is preferably in slurry form.

[0076] Examples of binders used as raw materials for fillers include methylcellulose, hydroxypropylmethylcellulose, hydroxypropoxylcellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinyl alcohol, and glycerin. Among these, it is preferable to use methylcellulose and hydroxypropoxylcellulose in combination. The binder content is preferably 0 to 25 parts by mass when the mass of the filler is 100 parts by mass.

[0077] The water content is preferably 15 to 75 parts by mass when the mass of the filler is 100 parts by mass.

[0078] Surfactants that can be used as raw materials for fillers include ethylene glycol, dextrin, fatty acid soap, and polyalcohol. These may be used individually or in combination of two or more. The surfactant content is preferably 0 to 15 parts by mass when the mass of the filler is 100 parts by mass.

[0079] The pore-forming material used as a raw material for the filler is not particularly limited as long as it becomes pore after firing, and examples include graphite, starch, foamed resin, superabsorbent resin, and silica gel. The content of the pore-forming material is preferably 0 to 85 parts by mass when the mass of the filler is 100 parts by mass.

[0080] There are no particular restrictions on the method of filling the slits formed in the honeycomb molded body with electrode material attached with the filler material, but one method is to fill the slits with the filler material using a syringe or the like. With this method, the filler material can be evenly filled into the slits. Of course, the filler material may also be filled into the slits using a spatula or the like.

[0081] After filling with the filler material, the binder and other contaminants in the filler material are removed by heat treatment. The heat treatment conditions are not particularly limited, but it is preferable to heat at 300 to 600°C for 0.5 to 5 hours in an atmospheric environment. [Examples]

[0082] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0083] <Examples 1-12 and Comparative Example 2> A ceramic powder containing silicon carbide (SiC) powder and the dopant particles shown in Table 1 was mixed with methylcellulose and hydroxypropoxylcellulose as binders, and a water-absorbing resin as a pore-forming agent, and then water was added to prepare a molding raw material. Next, the molding raw material was kneaded in a vacuum clay mixer to produce a cylindrical clay block. This block was then molded using an extrusion molding machine with a predetermined die structure to obtain a rectangular prism-shaped honeycomb molded body in which the shape of each cell in a cross section perpendicular to the flow direction of the cells was rectangular. This honeycomb molded body was then dried using high-frequency dielectric heating, and then dried in a hot air dryer at 120°C for 2 hours to produce a dried honeycomb body. Next, after degreasing the honeycomb dry material, a honeycomb sintered body was obtained by impregnating and firing the degreased honeycomb material with silicon (metallic silicon) doped with a dopant (boron: B) at 1500°C in a vacuum. Subsequently, an oxidation treatment was performed in air at the temperatures and times shown in Table 1. Note that no oxidation treatment was performed in Example 10. The honeycomb structure (ceramic body) obtained in this way was confirmed by cross-sectional observation with a scanning electron microscope (SEM) to have a matrix-domain structure in which silicon is the matrix and particles such as silicon carbide are the domains, and silicon was present as a continuous phase.

[0084] A paste for forming electrodes was prepared by mixing silicon carbide powder, boron nitride powder, methylcellulose, glycerin, and water in a rotary-rotating stirrer. The mixture consisted of 100 parts by mass of silicon carbide (SiC) powder, 0.5 parts by mass of methylcellulose, 10 parts by mass of glycerin, and 38 parts by mass of water. Next, this electrode-forming paste was applied to predetermined positions on a honeycomb structure and fired to obtain a honeycomb structure with electrodes.

[0085] <Comparative Example 1> A honeycomb structure with electrodes was fabricated in the same manner as described above, except that dopant particles were not incorporated into the molding material and oxidation treatment was not performed after impregnation and firing.

[0086] The honeycomb structure obtained above was evaluated as follows.

[0087] <Content of silicon carbide (SiC), silicon phase (Si), and silicon oxide film (SiO2) in honeycomb structures> According to the method described above, the content of silicon carbide (SiC), silicon phase (Si), and silicon oxide film (SiO2) in the honeycomb structure was determined.

[0088] <Porosity of honeycomb structures> The porosity of the honeycomb structure was determined according to the method described above.

[0089] <Dopant content in dopant particles> The dopant content in the dopant particles was determined according to the method described above. A Hitachi High-Tech S-3400N SEM was used, and a CAMECA NanoSIMS 50L SIMS was used.

[0090] <Concentration of dopant dissolved in silicon phase> The concentration of the dopant dissolved in the silicon phase was determined according to the method described above. A Hitachi High-Technologies Corporation PS3510DD ICP (Inductively Coupled Plasma) analyzer was used.

[0091] <Rate of Resistance Increase> Test samples were cut from the honeycomb structure obtained above, and the volume resistivity R0 of the test samples was measured. Next, these test samples were subjected to a 200-hour durability test at 950°C in a water vapor atmosphere, and the volume resistivity R1 of the test samples after the durability test was measured. Using these volume resistivity values, the resistance increase rate (R1 / R0) was calculated. In this evaluation, a ratio of R1 / R0 of 1.6 or less is represented as "AA," a ratio greater than 1.6 and less than or equal to 1.8 is represented as "A," a ratio greater than 1.8 and less than or equal to 2.0 is represented as "B," and a ratio greater than 2.0 is represented as "C." Note that if the resistance increase rate is less than a rating of "B," it can be said that the effect of suppressing resistance increase under high-temperature environments is high.

[0092] The results of each of the above evaluations are shown in Table 1.

[0093] [Table 1]

[0094] As shown in Table 1, the honeycomb structures (ceramic bodies) of Examples 1 to 12 had a lower resistance increase rate than those rated "B", indicating a high effectiveness in suppressing resistance increase under high-temperature environments. In contrast, the honeycomb structure of Comparative Example 1 did not contain dopant particles in the silicon phase, and therefore its effect in suppressing resistance increase under high-temperature conditions was insufficient. Furthermore, the honeycomb structure of Comparative Example 2 had too little silicon phase content and too high porosity, and therefore its effect in suppressing resistance increase under high-temperature conditions was insufficient.

[0095] As can be seen from the above results, the present invention provides a ceramic body that can be used in an electric heating heater that can continue to generate heat for a long period of time in a high-temperature environment. Furthermore, the present invention provides an electric heating heater that can continue to generate heat for a long period of time in a high-temperature environment. [Explanation of Symbols]

[0096] 1. Ceramic particles 2. Silicon Phase 3. Dopant particles 10 Honeycomb structure 10A First honeycomb structure 10B Second honeycomb structure 11 Peripheral wall 12 First end surface 13 Second end face 14 cells 15 Bulkhead 20 Pair of electrode sections 30 slits 31. First Slit 32. Second Slit 33 Third Slit 40 Filler 50 Conductive connector

Claims

1. Multiple ceramic particles comprising one or more selected from silicon carbide, silicon nitride, and aluminum nitride, A silicon phase in which the dopant is solid-dissolved exists between a plurality of the aforementioned ceramic particles, The silicon phase contains a plurality of dopant particles including a dopant A ceramic body containing, The dopant is a group 13 or group 15 element. The silicon phase content in the ceramic body is 20 to 80% by mass. A ceramic body having a porosity of 30% or less.

2. The ceramic body according to claim 1, wherein the silicon phase exists as a continuous phase.

3. The ceramic body according to claim 1 or 2, wherein the dopant content in the dopant particles in the ceramic body is 0.001% by mass or more.

4. The ceramic body according to claim 1 or 2, wherein a silicon oxide film is formed on at least a part of the surface and / or interior of the ceramic body, and the content of the silicon oxide film in the ceramic body is 0.1% by mass or more.

5. The concentration of the dopant dissolved in the silicon phase is 1 × 10 16 ~5 x 10 20 pieces / cm 3 The ceramic body according to claim 1 or 2.

6. The ceramic body according to claim 1 or 2, wherein the ceramic body is a honeycomb structure having an outer peripheral wall and partition walls disposed inside the outer peripheral wall and forming a plurality of cells extending from a first end face to a second end face.

7. A ceramic body according to claim 1 or 2, used in an electric heating heater.

8. An electric heating heater comprising the ceramic body described in claim 1 or 2.

9. The electric heating heater according to claim 8, further comprising a pair of electrode portions provided on the ceramic body, and electrode terminals connected to the pair of electrode portions.

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