Ceramic body and electric heating heater

Abstract

This invention provides a ceramic body and an electric heater, the ceramic body being used in an electric heater capable of continuous heating under high-temperature conditions. The ceramic body of this invention comprises: a plurality of ceramic particles (1) selected from silicon carbide, silicon nitride, and aluminum nitride; a silicon phase (2) existing between the plurality of ceramic particles (1) and containing a dopant; and a plurality of dopant particles (3) existing in the silicon phase (2) and containing the dopant. The dopant is a group 13 element or a group 15 element. The content of the silicon phase (2) in the ceramic body is 20% to 80% by mass. The porosity of the ceramic body is less than 30%.

Description

Technical Field

[0001] This invention relates to ceramic bodies and electrically heated heaters. Background Technology

[0002] Industrial heaters are used in various products and production equipment for heating objects. Among them, an electric heater with a honeycomb structure is known. This electric heater has electrodes mounted on a honeycomb structure made of conductive ceramic, and heats the honeycomb structure by passing an electric current through it.

[0003] For example, Patent Document 1 discloses a honeycomb structure containing particles 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% to 80% by mass, and the porosity is less than 30%. This honeycomb structure, by controlling the silicon doping amount, can suppress the generation of excess current.

[0004] Furthermore, Patent Document 2 discloses a honeycomb structure in which the partitions and outer peripheral walls are made of ceramic 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. This honeycomb structure exhibits an excellent balance between oxidation resistance and thermal shock resistance due to the presence of the specified oxide film.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2022-142543

[0008] Patent Document 2: Japanese Patent Application Publication No. 2022-145495 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] The honeycomb structures in Patent Documents 1 and 2 are primarily used as catalyst supports for purifying automobile exhaust and are not suitable for other applications. In particular, various industrial heaters sometimes require continuous heating at high temperatures (e.g., 600–1200°C), but the honeycomb structures in Patent Documents 1 and 2 are difficult to sustain at such high temperatures.

[0011] The present invention was made to solve the aforementioned problems, and its purpose is to provide a ceramic body that can be used in an electric heating heater capable of continuous heating for a long time in a high-temperature environment.

[0012] In addition, the purpose of this invention is to provide an electric heater that can generate heat continuously for a long time in a high-temperature environment.

[0013] Methods for solving problems

[0014] To enable electric heaters to maintain continuous heating at high temperatures for extended periods, it is necessary to suppress the increase in resistance of the ceramic body used in the heater at high temperatures. The inventors conducted in-depth research on ceramic bodies and obtained the following insights: the increase in resistance of the ceramic body at high temperatures is due to a decrease in the dopant concentration dissolved in the silicon phase. Therefore, the inventors discovered that by leaving the dopant as a solid phase (dopant particles) within the silicon phase existing between the ceramic particles, even with a decrease in the dopant concentration dissolved in the silicon phase at high temperatures, the dopant in the dopant particles remains dissolved in the silicon phase, thus maintaining the dopant concentration in the silicon phase. As a result, the increase in resistance can be suppressed, thus completing the present invention. That is, the present invention is illustrated below.

[0015] <1> A ceramic body containing:

[0016] It contains multiple ceramic particles selected from one or more of silicon carbide, silicon nitride, and aluminum nitride.

[0017] A silicon phase existing between multiple of the aforementioned ceramic particles and containing dopants in solid solution, and

[0018] Multiple dopant particles that exist in the silicon phase described above and contain dopants;

[0019] The aforementioned dopants are either group 13 or group 15 elements.

[0020] The content of the silicon phase in the above-mentioned ceramic body is 20% to 80% by mass.

[0021] The porosity of the aforementioned ceramic body is less than 30%.

[0022] <2> according to <1> The ceramic body wherein the silicon phase exists as a continuous phase.

[0023] <3> according to <1> or <2> The ceramic body wherein the content of the dopant in the dopant particles of the ceramic body is 0.001% by mass or more.

[0024] <4> according to <1> ~ <3> The ceramic body according to any one of the following methods, wherein a silicon oxide film is formed on at least a portion 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.

[0025] <5> according to <1> ~ <4> In any one of the ceramic bodies, the concentration of the dopant dissolved in the silicon phase is 1 × 10⁻⁶. 16 ~5×10 20 pcs / cm 3.

[0026] <6> according to <1> ~ <5> The ceramic body according to any one of the following methods is a honeycomb structure having an outer peripheral wall and a partition wall, wherein the partition wall is disposed on the inner side of the outer peripheral wall and is divided into a plurality of pores extending from a first end face to a second end face.

[0027] <7> according to <1> ~ <6> The ceramic body described in any one of the above is used in an electrically heated heater.

[0028] <8> An electric heating heater, which has <1> ~ <7> The ceramic body as described in any one of the following.

[0029] <9> according to <8> The electric heating heater further includes a pair of electrode portions disposed on the ceramic body and electrode terminals connected to the pair of electrode portions.

[0030] Invention Effects

[0031] According to the present invention, a ceramic body can be provided for use in an electric heating heater capable of continuous heating for a long period of time in a high-temperature environment.

[0032] Furthermore, according to the present invention, an electric heater capable of continuous heating under high-temperature conditions can be provided. Attached Figure Description

[0033] Figure 1 This is a partial schematic cross-sectional view of the ceramic body according to an embodiment of the present invention.

[0034] Figure 2 This is a perspective view of an electrically heated heater according to an embodiment of the present invention.

[0035] Figure 3 This is a front view of a surface orthogonal to the direction of the grid extension of another electric heating heater according to an embodiment of the present invention.

[0036] Explanation of reference numerals in the attached figures

[0037] 1: Ceramic particle, 2: Silicon phase, 3: Dopant particle, 10: Honeycomb structure, 10A: First honeycomb structure, 10B: Second honeycomb structure, 11: Outer peripheral wall, 12: First end face, 13: Second end face, 14: Hole grid, 15: Partition wall, 20: A pair of electrode sections, 30: Slit, 31: First slit, 32: Second slit, 33: Third slit, 40: Filler material, 50: Conductive connector. Detailed Implementation

[0038] The ceramic body of the present invention comprises: a plurality of ceramic particles containing one or more selected from silicon carbide, silicon nitride, and aluminum nitride; a silicon phase present among the plurality of ceramic particles and in which a dopant is dissolved; and a plurality of dopant particles present in the silicon phase and containing the dopant. The dopant is a group 13 or group 15 element. 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 configuring the ceramic body of the present invention as described above, even when the dopant concentration in the silicon phase decreases at high temperatures, the dopant in the dopant particles remains dissolved in the silicon phase, thus maintaining the dopant concentration in the silicon phase (particularly at the solid solution limit). As a result, the increase in resistance of the ceramic body at high temperatures can be suppressed, and when used in an electrically heated heater, it can sustain heating at high temperatures for extended periods.

[0039] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings. It should be understood that the present invention is not limited to the following embodiments. Without departing from the spirit of the present invention, appropriate modifications, improvements, etc., to the following embodiments based on ordinary knowledge of those skilled in the art also fall within the scope of the present invention.

[0040] Figure 1 This is a partial schematic cross-sectional view of the ceramic body according to an embodiment of the present invention.

[0041] like Figure 1 As shown, the ceramic body of the embodiment of the present invention contains ceramic particles 1, silicon phase 2, and dopant particles 3. It should be noted that... Figure 1 The example shows that pores can exist even when the porosity of the ceramic body is 0% (no pores).

[0042] The ceramic particles 1 comprise one or more selected from silicon carbide, silicon nitride, and aluminum nitride. These ceramic particles 1 function as aggregate particles in the ceramic body, thus enabling the ceramic body to be robust. In particular, if the main component of the ceramic particles 1 is silicon carbide, the thermal conductivity is higher, and the difference in thermal expansion coefficients with the silicon phase 2 is smaller, which is therefore preferable. It should be noted that silicon carbide being the main component of the ceramic particles 1 means that the proportion of silicon carbide in the ceramic particles 1 is 80% by mass or more, preferably 90% by mass or more.

[0043] The proportions of each component in ceramic particle 1 are determined as follows: ceramic particle 1 is determined by observing the cross-section of the ceramic body, and the amount of each component contained in ceramic particle 1 is determined by measuring the amount of each component in ceramic particle 1 using the fluorescence X-ray method.

[0044] Silicon phase 2 exists between multiple ceramic particles 1 and contains dopants dissolved in it. By dissolving the dopants in silicon phase 2, the volume resistivity of the ceramic mass can be effectively reduced.

[0045] The content of silicon phase 2 in the ceramic body is 20% to 80% by mass. By setting the content of silicon phase 2 to 20% by mass or more, the volume resistivity of the ceramic body is reduced, thereby effectively suppressing the generation of excess current, and the balance between the strength and Young's modulus of the ceramic body becomes better, thus improving thermal shock resistance. In addition, by setting the content of silicon phase 2 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 content of silicon phase 2 in the ceramic body is preferably 30% to 80% by mass, more preferably 40% to 80% by mass.

[0046] The content of silicon phase 2 in the ceramic body is determined as follows. First, the amount of silicon is measured in a cross-section of the ceramic body using fluorescence X-ray diffraction. The measured amount of silicon includes not only the amount of silicon in silicon phase 2 but also the amount of silicon contained in the ceramic particles 1 (silicon carbide, silicon nitride, etc.). Therefore, the value obtained by subtracting the measured amount of silicon in the ceramic particles 1 from the measured amount of silicon is taken as the content of silicon phase 2. It should be noted that, in the case where a silicon oxide film is formed on at least a portion of the surface and / or interior of the ceramic body (described later), the amount of silicon measured by fluorescence X-ray diffraction 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 value obtained by further subtracting this amount of silicon is taken as the content of silicon phase 2.

[0047] In the ceramic body, silicon phase 2 is preferably present as a continuous phase. If silicon phase 2 is a continuous phase, it is easier to control the volume resistivity of the ceramic body to be low. Here, the existence of silicon phase 2 as a continuous phase refers to a matrix-domain structure with silicon phase 2 as the matrix and ceramic particles 1 as domains.

[0048] The dopants dissolved in silicon phase 2 are group 13 or group 15 elements.

[0049] 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. If the dopant dissolved in silicon phase 2 is an element from the same group, it can exhibit conductivity without being affected by reverse doping, therefore, multiple elements can be included. As a dopant, it is preferable to select one or both of B and Al, or one or both of N and P.

[0050] The concentration of the dopant dissolved in silicon phase 2 can be adjusted appropriately according to the required volume resistivity of the ceramic body, and is not particularly limited, but preferably 1×10⁻⁶. 16 ~5×10 20 pcs / cm 3 More preferably 5×10 17 ~5×10 20 pcs / cm3 By controlling the concentration of the dopant within this range, the volume resistivity of the ceramic body can be easily reduced. Generally, there is a tendency that if the concentration of the dopant dissolved in silicon phase 2 increases, the volume resistivity of the ceramic body decreases, and if the concentration of the dopant dissolved in silicon phase 2 decreases, the volume resistivity of the ceramic body increases.

[0051] The concentration of dopants dissolved in silicon phase 2 can be determined using the silicon separation ICP-ELISA method specified in JIS G 1322-3:2010 "Methods for Analysis of Metallic Silicon". Specifically, the ceramic body is decomposed with nitric acid and hydrofluoric acid, perchloric acid is added, and heating produces white fumes from the perchloric acid, causing the silicon to volatilize and separate as silicon tetrafluoride. The salts are then dissolved in water. Next, the boron content in the solution is determined using ICP-ELISA, and the boron concentration in the silicon is calculated. This calculated boron concentration is taken as the concentration of boron dissolved in silicon phase 2. It should be noted that dopants other than boron can also be determined using the same method.

[0052] Dopant particles 3 are present in silicon phase 2 and contain dopants. The type of dopant is the same as that dissolved in silicon phase 2. Therefore, the dopants contained in dopant particles 3 are either group 13 or group 15 elements. By having dopant particles 3 present in silicon phase 2, even if the dopant concentration dissolved in silicon phase 2 decreases at high temperatures, the dopant in dopant particles 3 will remain dissolved in silicon phase 2, thus maintaining the dopant concentration in the silicon phase (especially at the solid solution limit). As a result, the increase in resistance of the ceramic body at high temperatures can be suppressed, and when used in electrically heated heaters, it can sustain heating at high temperatures for extended periods.

[0053] Dopant particles 3 can exist in silicon phase 2 in the form of various compounds. Specifically, they can exist in silicon phase 2 in the form of compounds such as carbides, nitrides, and borides. Examples of such compounds include B4C, TiB2, BN, AlN, GaN, InN, and Al4C3.

[0054] 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 such a range, it is possible to stably ensure that the dopant in the dopant particles 3 is dissolved in the silicon phase 2 under high temperature conditions, thereby maintaining the dopant concentration in the silicon phase (especially maintaining it at the solid solution limit).

[0055] The higher the dopant content in the dopant particles 3 in the ceramic body, the easier it is to achieve the above-mentioned effect. Therefore, there is no specific upper limit, such as below 5.000% by mass, below 4.000% by mass, or below 3.000% by mass. If the dopant content in the dopant particles 3 in the ceramic body is within such a range, it is difficult to reduce the strength and other properties of the ceramic body.

[0056] The dopant content in dopant particles 3 within the ceramic body can be determined using the following method. First, a total of five samples are selected from the vicinity of the center along the height and radial directions of the ceramic body. The size of each sample is set to 1 cm. 3 The sample was sized as a cube (1cm × 1cm × 1cm). The sample was observed at 1000x magnification using SEM (Scanning Electron Microscopy) to identify dopant particles 3. Then, SIMS (Secondary Ion Mass Spectrometry) was used to analyze the dopant particles 3 and determine their content within the ceramic body. The average content of the dopant particles 3 in the five samples was taken as the result of the dopant content in the ceramic body.

[0057] The porosity of the ceramic body is 30% or less. By keeping the porosity of the ceramic body below 30%, the thermal conductivity of the ceramic body is increased, and therefore the thermal shock resistance is also improved. From the viewpoint of consistently ensuring this effect, the porosity of the ceramic body is preferably 20% or less, more preferably 10% or less. The lower limit of the porosity of the ceramic body is not particularly limited, and can be 0% (no pores).

[0058] It should be noted that the porosity of the ceramic body is a value measured by a mercury porosimeter.

[0059] Preferably, a silica film is formed on at least a portion of the ceramic body's surface and / or interior. Furthermore, the silica film content in the ceramic body is preferably 0.1% by mass or more. By forming a silica film on at least a portion of the ceramic body's surface and / or interior, the balance between the ceramic body's oxidation resistance and thermal shock resistance at high temperatures can be improved. From the viewpoint of consistently ensuring this effect, the silica film content in the ceramic body is preferably 0.2% by mass or more, more preferably 0.3% by mass or more. It should be noted that the upper limit of the silica film content in the ceramic body is not particularly limited, and for example, it can be 5.0% by mass, 4.0% by mass, or 3.0% by mass.

[0060] Here, the surface of the ceramic body capable of forming a silicon oxide film refers to the surface of the ceramic body exposing silicon. Furthermore, the interior of the ceramic body capable of forming a silicon oxide film refers to the pore surface of the ceramic body exposing silicon.

[0061] Regarding the content of silica film in ceramic bodies, the amount of oxygen element determined by the inactive gas melting infrared absorption method is assumed to be entirely due to the silica film. The content of silica film in ceramic bodies can be calculated by molecular weight calculation.

[0062] The shape of the ceramic body is not particularly limited and can be appropriately adjusted according to the application of the electric heating heater. For example, the shape of the ceramic body can be designed as a honeycomb structure. A ceramic body with a honeycomb structure (hereinafter referred to as a "honeycomb structure") can have an outer peripheral wall and partitions, with the partitions disposed on the inner side of the outer peripheral wall, dividing to form multiple cells extending from a first end face to a second end face. By forming a honeycomb structure, it is possible to easily heat the fluid flowing within the cells.

[0063] The ceramic body can be manufactured using well-known methods. For example, the ceramic body can be manufactured using the methods described below.

[0064] For example, firstly, a molding raw material is prepared by adding binders, surfactants, water, etc., to ceramic powder containing ceramic particles 1 and dopant particles 3.

[0065] Examples of binders include methylcellulose, hydroxypropyl methylcellulose, hydroxypropoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, and polyvinyl alcohol. Among these, methylcellulose and hydroxypropoxycellulose are preferred in combination. When the mass of the ceramic powder is set to 100 parts by mass, the binder content is preferably 2.0 to 10.0 parts by mass.

[0066] When the mass of ceramic powder is set to 100 parts by mass, the water content is preferably 20 to 60 parts by mass.

[0067] Surfactants such as ethylene glycol, dextrin, fatty acid soaps, and polyols can be used. They can be used alone or in combination of two or more. When the mass of the ceramic powder is set to 100 parts by mass, the surfactant content is preferably 0.1 to 2.0 parts by mass.

[0068] Pore-forming materials can be added to the molding raw materials as needed. Examples of pore-forming materials include starch, foaming resin, and water-absorbing resin.

[0069] Next, the obtained molding raw materials are mixed to form a blank, which is then molded to produce a ceramic molded body. In particular, in the case of producing a honeycomb structure ceramic molded body (hereinafter referred to as "honeycomb molded body"), the blank is extruded to produce an unprocessed (unfired) honeycomb molded body. In extrusion molding, a die with a desired overall shape, pore shape, partition wall thickness, pore density, etc., can be used.

[0070] Next, the obtained ceramic molded body (honeycomb molded body) is dried and degreased to produce a ceramic degreased body (honeycomb degreased body). The degreasing process is carried out at 300-500°C under atmospheric, inert, or reduced pressure atmospheres. Then, in a reduced pressure inert gas or vacuum, silicon (metallic silicon) with a dopant dissolved in it is impregnated into the ceramic degreased body (honeycomb degreased body) and fired. Through this impregnation firing, the pores in the ceramic degreased body (honeycomb degreased body) are filled and solidified by molten silicon, thereby enabling the porosity of the ceramic body (honeycomb structure) to be less than 30%. Examples of inert atmospheres include nitrogen atmosphere, rare gas atmospheres such as argon, or mixtures thereof. Examples of impregnation firing methods for silicon with a dopant dissolved in it include methods that involve placing a block of silicon containing a dopant dissolved in it in contact with the ceramic degreased body (honeycomb degreased body) and firing it.

[0071] To ensure thorough sintering, the firing temperature is preferably 1350°C or higher, more preferably 1400°C or higher, and even more preferably 1450°C or higher. Furthermore, to reduce manufacturing costs during firing, the firing temperature is preferably 2200°C or lower, more preferably 1800°C or lower, and even more preferably 1600°C or lower.

[0072] To ensure thorough sintering, the heating time of the ceramic degreased body (honeycomb degreased body) at the above-mentioned 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 of the ceramic degreased body (honeycomb degreased body) at the above-mentioned firing temperature is preferably 5 hours or less, more preferably 4 hours or less, and even more preferably 3 hours or less.

[0073] Furthermore, after impregnation firing, to improve durability, it is preferable to perform an oxidation treatment at 1000~1350°C for 1~300 hours. Oxidation treatment refers to heat treatment in an oxidizing atmosphere (e.g., under atmospheric conditions). By performing such heat treatment, a silica film can be formed on at least a portion of the surface and / or interior of the ceramic body (honeycomb structure).

[0074] The ceramic body of the present invention can generate heat using Joule heating by passing an electric current. Furthermore, even when the dopant concentration in the silicon phase 2 decreases at high temperatures, the dopant in the dopant particles 3 remains dissolved in the silicon phase 2, thus maintaining the dopant concentration in the silicon phase (particularly at the solid solution limit). Therefore, the ceramic body of the present invention can be used in an electrically heated heater, which can continuously generate heat for extended periods at high temperatures.

[0075] The electric heater according to an embodiment of the present invention includes the ceramic body described above. An example of this electric heater is shown below. Figure 2 . Figure 2 This is a perspective view of an electrically heated heater according to an embodiment of the present invention.

[0076] Figure 2 The electric heating heater shown includes a ceramic body with a honeycomb structure (hereinafter referred to as "honeycomb structure part 10"), a pair of electrode parts 20, a slit 30 and a filling material 40.

[0077] The honeycomb structure 10 has an outer peripheral wall 11 and partition walls 15. The partition walls 15 are disposed on the inner side of the outer peripheral wall 11 and divide it into a plurality of cells 14 extending from the first end face 12 to the second end face 13. The plurality of cells 14 form a flow path for fluid. A pair of electrode portions 20 are disposed on the outer peripheral 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. It should be noted that in Figure 1 The image shows an example where the entire space of the slit 30 is filled with the filling material 40, but the filling material 40 may also fill only a portion of the space of the slit 30.

[0078] The honeycomb structure having the structure described above can generate heat in the honeycomb structure 10 by allowing current to flow from a pair of electrode portions 20 to the honeycomb structure portion 10 using Joule heating.

[0079] When the main component of the honeycomb structure 10 is silicon carbide or a silicon-silicon carbide composite material, the filler material 40 preferably contains 20% by mass or more silicon carbide, more preferably 20 to 70% by mass. This allows the coefficient of thermal expansion of the filler material 40 to be close to that of the honeycomb structure 10, improving the thermal shock resistance of the honeycomb structure 10. The filler material 40 may also contain 30% by mass or more silicon dioxide, alumina, etc. The Young's modulus of the filler material 40 is preferably 500 kPa or more and 1500 MPa or less. By setting it within this range, stress buffering can be effectively utilized using the slits 30 during thermal shock, and the mechanical strength of the slits 30 can be maintained, suppressing defects and cracks during manufacturing and use. From the viewpoint of consistently ensuring this effect, the Young's modulus of the filler material 40 is more preferably 10 to 1000 MPa.

[0080] The honeycomb structure portion 10 has a columnar shape and a thickness in the direction in which the cells 14 extend. The ratio (length-to-width ratio) of the length of the cells 14 in the direction in which they extend to the width or diameter of each end face (first end face 12, second end face 13) is not particularly limited. Alternatively, the columnar shape may include a shape (flat shape) in which the length of the cells 14 in the direction in which they extend is shorter than the width or diameter of each end face (first end face 12, second end face 13).

[0081] The shape of the honeycomb structure section 10 is not particularly limited. For example, it can be a columnar shape with rounded end faces, an elliptical end face, or a polygonal shape (quadrilateral, pentagonal, hexagonal, heptagonal, octagonal, etc.) end face, or other shapes. It should be noted that... Figure 2 The honeycomb structure portion 10 is shown as an example of a columnar shape with quadrilateral (rectangular) end faces. Furthermore, for the purpose of improving heat resistance (suppressing cracks generated in the circumferential direction of the outer peripheral wall 11), the size of the honeycomb structure portion 10 is preferably such that the area of ​​each end face is 2000 to 65000 mm². 2 More preferably, it is 5000~25000mm 2 .

[0082] The shape of the perforations 14 in the surface (end face or cross-section of the honeycomb structure portion 10) orthogonal to the direction in which the perforations 14 extend is not particularly limited, and examples include quadrilaterals, hexagons, octagons, or combinations thereof. Among these, the shape of the perforations 14 is preferably quadrilateral or hexagonal. With such a shape of perforations 14, the pressure loss when fluids such as exhaust gas flow through the honeycomb structure portion 10 can be reduced.

[0083] The thickness of the outer peripheral wall 11 is not particularly limited. From the viewpoint of ensuring the structural strength of the honeycomb structure 10 and suppressing the leakage of fluid flowing in the pores 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 too thick, it becomes too strong, and sometimes it loses the strength balance with the partition wall 15, resulting in reduced thermal shock resistance. Therefore, 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.

[0084] It should be noted that the thickness of the outer peripheral wall 11 refers to the thickness of the portion of the outer peripheral wall 11 to be measured relative to the normal direction of the tangent of the outer peripheral wall 11 when the portion to be measured is observed from a plane orthogonal to the direction of the extension of the lattice 14.

[0085] The thickness of the partition wall 15 is not particularly limited, but is preferably 0.05 to 0.8 mm, more preferably 0.1 to 0.6 mm. By setting the thickness of the partition wall 15 to 0.05 mm or more, the reduction in strength of the honeycomb structure portion 10 can be suppressed. By setting the thickness of the partition wall 15 to 0.8 mm or less, when the honeycomb structure portion 10 is used as a catalyst carrier, the increase in pressure loss when the exhaust gas flows through can be suppressed.

[0086] It should be noted that, in this specification, the thickness of the partition 15 refers to the length of the portion of the line segment that connects the centroids of adjacent holes 14 in a plane orthogonal to the direction in which the holes 14 extend, passing through the partition 15.

[0087] The pore density of the honeycomb structure 10 is not particularly limited, but is preferably 4 to 150 pores / cm². 2 More preferably, 7~100 pores / cm 2 By controlling the pore density within this range, pressure loss when fluids such as exhaust gases flow through it can be reduced.

[0088] It should be noted that, in this specification, the cell density refers to the value obtained by dividing the number of cells by the area of ​​one end face of the honeycomb structure portion 10 excluding the outer peripheral wall 11.

[0089] The slit 30 provided in the honeycomb structure portion 10 is formed by missing or removing the outer peripheral wall 11 and / or the partition wall 15. The slit 30 can extend from the first end face 12 of the honeycomb structure portion 10 to the second end face 13.

[0090] A pair of electrode portions 20 are formed of a conductive material. The conductive material used in the pair of electrode portions 20 is not particularly limited, but is preferably an oxide ceramic or a metal, or a mixture of a metal compound and an oxide ceramic. The metal can be any elemental metal or alloy, such as silicon, aluminum, iron, stainless steel, titanium, tungsten, Ni-Cr alloys, etc. The metal compound is a substance other than an oxide ceramic, and examples include metal oxides, metal nitrides, metal carbides, metal silicides, metal borides, composite oxides, etc., such as FeSi2, CrSi2, alumina, silicon dioxide, titanium oxide, etc. It should be noted that the metal and metal compound can be a single type, or two or more can be used together. Specifically, examples of oxide ceramics include glass, cordierite, mullite, etc. Glass may further comprise an oxide composed of at least one component selected from B, Mg, Al, Si, P, Ti, and Zr.

[0091] 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 the above 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 resistance is properly controlled, and heating is more uniform. If the thickness of the pair of electrode portions 20 is 5 mm or less, the possibility of breakage is reduced.

[0092] It should be noted that, in this specification, the thickness of a pair of electrode portions 20 refers to the thickness in the normal direction of the tangent to the outer surface of the pair of electrode portions 20 when the portion to be measured is observed from a surface orthogonal to the direction in which the hole grid 14 extends.

[0093] The 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 preferably 5×10 -7 ~2.5×10 -1 Ω·m, further preferably 1×10 -6 ~1.25×10 -1 Ω·m. Specifically, by setting the resistivity of the pair of electrode sections 20 to 5 × 10⁻⁶ Ω·m. -1 Below Ω·m, the resistance during electric heating can be reduced.

[0094] It should be noted that, in this specification, the resistivity of the pair of electrode sections 20 refers to the value measured at 400°C using the four-terminal method.

[0095] The positions of the pair of electrode portions 20 are not particularly limited, as long as they are on the outer peripheral wall 11 of the honeycomb structure portion 10. Similarly, the positions of the slits 30 provided in the honeycomb structure portion 10 are not particularly limited. For example, in one embodiment of the honeycomb structure, such as Figure 2 As shown, a pair of electrode portions 20 are disposed on a plane of the outer peripheral wall 11 of the quadrangular 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.

[0096] like Figure 2 As shown, the slit 30 may further include a second slit 32 and a third slit 33. The second slit 32 extends inward from two outer peripheral walls 11 orthogonal to the outer peripheral walls 11 on which a pair of electrode portions 20 are disposed. The third slit 33 intersects the first slit 31 but does not reach the outer peripheral walls 11. In this case, it is preferable that the second slit 32 and the third slit 33 are arranged alternately. By configuring it in this way, as... Figure 2 As shown by the arrow in the honeycomb structure 10, the current flows while meandering along the second slit 32 and the third slit 33, thus making it easy for the honeycomb structure to heat up evenly.

[0097] Alternatively, the cellular structure may have multiple cellular structure parts 10, which are connected by conductive connectors 50. Figure 3 The image shows a front view of a surface of an electrically heated heater with such a structure, orthogonal to the direction in which the perforations extend.

[0098] Figure 3The illustrated electric heater has a first honeycomb structure 10A and a second honeycomb structure 10B, which are connected by a conductive connector 50. With this structure, the current flows while meandering along the second slit 32 and the third slit 33 of the first and second honeycomb structures 10A and 10B, thus facilitating uniform heating of the electric heater.

[0099] Two conductive connectors 50 are provided on the outer peripheral walls 11 opposite to the first honeycomb structure portion 10A and the second honeycomb structure portion 10B. Specifically, the two conductive connectors 50 are respectively partially provided on the outer peripheral walls 11 at positions orthogonal to the first slit 31 and not crossing the first slit 31.

[0100] Various materials can be used as the material for the conductive connector 50, such as Si-SiC composite materials, Si-SiC composite materials impregnated with Si metal, etc.

[0101] Electrode terminals (not shown) may also be connected to a pair of electrode sections 20 as needed. The shape of the electrode terminals is arbitrary, and the electrode terminals may be columnar. By applying voltage to the honeycomb structure through the electrode terminals, the honeycomb structure can be easily heated using Joule heating. It should be noted that the applied voltage is preferably 12~900V, more preferably 48~600V, but the applied voltage can be appropriately varied.

[0102] The electrode terminals can be made of ceramic or carbon. If the electrode terminals are made of ceramic, they can be electrically connected to the honeycomb structure. Alternatively, metal terminals can be attached to the front end of each electrode terminal. The connection between ceramic or carbon electrode terminals and metal terminals can be achieved through riveting, welding, or using conductive adhesives. Conductive metals such as iron alloys and nickel alloys can be used as the material for the metal terminals.

[0103] The ceramic used to constitute the electrode terminal is not particularly limited, and examples include silicon carbide (SiC); metal compounds such as tantalum silicide (TaSi2) and chromium silicide (CrSi2); and composite materials containing one or more metals (cermets). Specific examples of cermets include composite materials of silicon metal and silicon carbide, composite materials of tantalum silicide or chromium silicide and silicon metal and silicon carbide, and composite materials obtained by adding one or more insulating ceramics such as alumina, mullite, zirconium oxide, cordierite, silicon nitride, and aluminum nitride to one or more of the aforementioned metals from the viewpoint of reducing thermal expansion. The carbon used to constitute the electrode terminal is preferably carbon-based. Carbon-based means that the carbon content is 50% by mass or more relative to the total components constituting the electrode terminal. The carbon content is more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0104] Additionally, a catalyst can be supported on the outer peripheral wall 11 of the honeycomb structure 10 facing the partition wall 15 or the pore 14, as needed. Various catalysts can be used, such as three-way catalysts and / or nickel oxide. By supporting the catalyst, purification performance can be achieved when waste gas or the like flows through the pore 14.

[0105] The manufacturing method of the electric heating heater according to the embodiments of the present invention is not particularly limited as long as it can manufacture a honeycomb structure having the above-described features. Hereinafter, an example of the manufacturing method of the electric heating heater according to the embodiments of the present invention will be described.

[0106] The method for manufacturing a honeycomb structure according to the embodiments of the present invention includes: step S1, obtaining a honeycomb molded body with electrode part raw material; step S2, forming slits; step S3, firing the honeycomb molded body; and step S4, filling with raw material for filler material.

[0107] Step S1 is a process of coating an electrode forming material onto a honeycomb molded body, which serves as a precursor to the honeycomb structure section 10, to obtain a honeycomb molded body with electrode forming material. Here, the honeycomb molded body refers to the honeycomb structure section 10 used to manufacture the aforementioned honeycomb structure section 10 before firing, which can be manufactured by the method described above.

[0108] Next, electrode forming 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, the electrode forming materials are preferably formed by adding predetermined additives to silicon carbide powder and silicon powder and then mixing them. Next, the obtained electrode forming materials are coated onto predetermined positions on the outer peripheral wall 11 of the dried honeycomb molded body (dried honeycomb body) to obtain a honeycomb molded body with electrode forming materials. The method for preparing the electrode forming materials and the method for coating the electrode forming materials onto the honeycomb molded body can be performed according to known methods for manufacturing honeycomb structures.

[0109] Alternatively, as another manufacturing method, the honeycomb molded body can be temporarily fired in step S1 before the electrode forming material is coated. That is, in other manufacturing methods, the honeycomb molded body is fired to produce a fired honeycomb body, and the electrode forming material is coated on the fired honeycomb body to obtain a fired honeycomb body with electrode forming material instead of a honeycomb molded body with electrode forming material.

[0110] Step S2 is a process in which slits are formed at predetermined positions in a honeycomb molded body containing electrode material. The slits are preferably formed using a rotary cutter or the like. The slits are formed by opening at predetermined positions in the honeycomb molded body containing electrode material.

[0111] Step S3 is a process of firing a honeycomb molded body with electrode material to obtain a fired honeycomb body. Before firing, the honeycomb molded body with electrode material can be dried. Additionally, pre-firing can be performed before firing to remove binders and other contaminants from the filler material. As firing conditions, heating at 1400–1500°C for 1–20 hours in an inert atmosphere such as nitrogen or argon is preferred. Furthermore, after firing, to improve durability, oxidation treatment at 1200–1350°C for 1–300 hours is preferred. The pre-firing and firing methods are not particularly limited; electric furnaces, gas furnaces, etc., can be used for firing.

[0112] In addition, in the S3 process, the honeycomb molded body with electrode parts can be heat-treated at 300~1500℃. This heat treatment can be the heat treatment included in the pre-firing and firing processes described above, or it can be performed separately from the pre-firing and firing processes.

[0113] Step S4 is a process of filling the slits formed in the sintered honeycomb body with raw materials for filler material. In step S4, firstly, raw materials for filler material are prepared. Raw materials for filler material are the materials used to produce the aforementioned filler material. For example, raw materials for insulating material can be obtained by kneading a mixture obtained by mixing an adhesive, surfactant, pore-forming material, water, etc., with the aforementioned filler material. The raw materials for filler material are preferably in the form of a slurry.

[0114] Examples of binders used as raw materials for filler materials include methylcellulose, hydroxypropyl methylcellulose, hydroxypropoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, polyvinyl alcohol, and glycerin. Among these, methylcellulose and hydroxypropoxycellulose are preferably used together. When the mass of the filler material is set to 100 parts by mass, the binder content is preferably 0 to 25 parts by mass.

[0115] When the mass of the filler material is set to 100 parts by mass, the water content is preferably 15 to 75 parts by mass.

[0116] Surfactants used as raw materials for filler materials can include ethylene glycol, dextrin, fatty acid soaps, polyols, etc. They can be used individually or in combination of two or more. When the mass of the filler material is set to 100 parts by mass, the surfactant content is preferably 0 to 15 parts by mass.

[0117] The pore-forming material used as a raw material for filler materials is not particularly limited as long as it becomes porous after firing; examples include graphite, starch, foaming resin, water-absorbing resin, and silica gel. When the mass of the filler material is set to 100 parts by mass, the content of the pore-forming material is preferably 0 to 85 parts by mass.

[0118] There are no particular limitations on the method for filling the slits formed in the honeycomb molded body with electrode material into the filler material. For example, a syringe or similar device can be used to fill the slits with the filler material. This method allows for uniform filling of the slits with the filler material. Alternatively, a scraper or similar tool can be used to fill the slits with the filler material.

[0119] After filling the raw materials for the filler material, the binder and other components in the raw materials are removed by heat treatment. There are no particular limitations on the heat treatment conditions, but heating at 300-600°C for 0.5-5 hours in an atmospheric atmosphere is preferred.

[0120] Example

[0121] The present invention will be described in more detail below by way of examples, but the present invention is not limited to these examples in any way.

[0122] <Examples 1-12 and Comparative Example 2>

[0123] A molding raw material is prepared by adding methylcellulose and hydroxypropoxycellulose as binders and a water-absorbing resin as a pore-forming material to a ceramic powder containing silicon carbide (SiC) powder and dopant particles as shown in Table 1, and then adding water.

[0124] Next, the raw materials are mixed using a vacuum ply mill to produce cylindrical blanks. These blanks are then formed using an extrusion molding machine with a predetermined die structure, resulting in a quadrangular prism-shaped honeycomb molded body with quadrilateral cells in a cross-section perpendicular to the flow path direction of the cells. This honeycomb molded body is then dried using high-frequency induction heating and a hot air dryer at 120°C for 2 hours to produce a dried honeycomb body.

[0125] Next, after degreasing the honeycomb dried body, silicon (metallic silicon) doped with a dopant (boron:B) was impregnated and sintered in the degreased honeycomb body under vacuum at 1500°C, thereby obtaining a sintered honeycomb body. Then, it was oxidized in the atmosphere at the temperatures and times shown in Table 1. It should be noted that no oxidation treatment was performed for Example 10. The honeycomb structure (ceramic body) thus obtained has a matrix-domain structure with silicon as the matrix and particles such as silicon carbide as domains, which can be confirmed by cross-sectional observation using a scanning electron microscope (SEM), showing that silicon exists as a continuous phase.

[0126] An electrode forming paste was prepared by mixing silicon carbide powder, boron nitride powder, methylcellulose, glycerol, and water using a rotary mixer. Specifically, when the silicon carbide (SiC) powder was 100 parts by weight, the methylcellulose was 0.5 parts by weight, the glycerol was 10 parts by weight, and the water was 38 parts by weight. The electrode forming paste was then applied to predetermined positions on a honeycomb structure and sintered to obtain a honeycomb structure with electrodes.

[0127] <Comparative Example 1>

[0128] No dopant particles are incorporated into the molding raw material. In addition, no oxidation treatment is performed after impregnation and firing. Otherwise, the same operation as described above is used to fabricate a honeycomb structure with electrode sections.

[0129] The honeycomb structure obtained above is evaluated as follows.

[0130] <Content of silicon carbide (SiC), silicon phase (Si), and silicon oxide film (SiO2) in the honeycomb structure>

[0131] Based on the above method, the contents of silicon carbide (SiC), silicon phase (Si), and silicon oxide film (SiO2) in the honeycomb structure are determined.

[0132] <Porosity of honeycomb structures>

[0133] The porosity of the honeycomb structure is calculated using the method described above.

[0134] <Dopant content in dopant particles>

[0135] Following the method described above, the dopant content in the dopant particles was determined. For the SEM, a Hitachi High Technology S-3400N was used, and for the SIMS, a CAMECA NanoSIMS 50L was used.

[0136] <Concentration of dopants dissolved in the silicon phase>

[0137] Following the method described above, the concentration of the dopant dissolved in the silicon phase was determined. As the ICP (inductively coupled plasma) analysis device, a PS 3510 DD model manufactured by Hitachi Advanced Technology Co., Ltd. was used.

[0138] <Rate of resistance rise>

[0139] Test samples were cut from the honeycomb structure obtained above, and the volume resistivity R0 of the test samples was measured. Next, the test samples were subjected to a durability test at 950°C for 200 hours in a water vapor atmosphere, and the volume resistivity R1 of the test samples after the durability test was measured. The rate of increase in resistance (R1 / R0) was calculated using these volume resistivity values.

[0140] In this evaluation, R1 / R0 below 1.6 is designated as "AA", R1 / R0 above 1.6 but below 1.8 is designated as "A", R1 / R0 above 1.8 but below 2.0 is designated as "B", and R1 / R0 above 2.0 is designated as "C". It should be noted that if the rate of resistance increase is less than evaluation "B", it can be said that the effect of suppressing resistance increase under high-temperature conditions is high.

[0141] The evaluation results are shown in Table 1.

[0142] [Table 1]

[0143]

[0144] As shown in Table 1, the resistance rise rate of the honeycomb structure (ceramic body) in Examples 1 to 12 is less than that of the evaluation "B", and the effect of suppressing the resistance rise under high temperature environment is high.

[0145] In contrast, the honeycomb structure of Comparative Example 1 did not contain dopant particles in the silicon phase, thus its effect on suppressing the increase in resistance under high-temperature conditions was insufficient. Furthermore, the honeycomb structure of Comparative Example 2 had too little silicon phase and too high porosity, thus its effect on suppressing the increase in resistance under high-temperature conditions was also insufficient.

[0146] As can be seen from the above results, according to the present invention, a ceramic body for use in an electric heating heater capable of continuous heating for a long period of time in a high-temperature environment can be provided. Furthermore, according to the present invention, an electric heating heater capable of continuous heating for a long period of time in a high-temperature environment can be provided.

Claims

1. A ceramic body comprising: It contains multiple ceramic particles selected from one or more of silicon carbide, silicon nitride, and aluminum nitride. A silicon phase existing between multiple ceramic particles and containing dopants in solid solution, and Multiple dopant particles present in the silicon phase and containing dopants; The dopant is a group 13 element or a group 15 element. The silicon phase in the ceramic body is 20-80% by mass. The porosity of the ceramic body is less than 30%.

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 content of the dopant in the dopant particles of 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 portion 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 ceramic body according to claim 1 or 2, wherein, The concentration of the dopant dissolved in the silicon phase is 1 × 10⁻⁶. 16 ~5×10 20 pcs / cm 3 .

6. The ceramic body according to claim 1 or 2, wherein, The ceramic body is a honeycomb structure having an outer peripheral wall and partitions, wherein the partitions are disposed on the inner side of the outer peripheral wall and are divided into multiple pores extending from the first end face to the second end face.

7. The ceramic body according to claim 1 or 2, used in an electrically heated heater.

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

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

Images