Silicon-carbide-based ceramic honeycomb structure

Abstract

This silicon-carbide-based ceramic honeycomb structure has a plurality of flow paths separated by porous partition walls so as to pierce from a first end surface to a second end surface and has a coefficient of thermal expansion (between room temperature and 800°C) of 49×10-7 / °C or less. The partition walls each comprise aggregates comprising silicon carbide, an SiO2 layer present on surfaces of the aggregates, and a binder phase comprising a cordierite phase and a spinel phase. The aggregates have portions where the aggregates are bonded to one another with the SiO2 layer without via the binder phase and portions where the aggregates are bonded to one another with the SiO2 layer via the binder phase. The SiO2 layer comprises an amorphous SiO2 phase and a crystalline SiO2 phase.

Description

Silicon carbide ceramic honeycomb structure

[0001] The present invention relates to a silicon carbide ceramic honeycomb structure used in a ceramic honeycomb filter for removing particulate matter (hereinafter simply referred to as "PM") and the like from exhaust gas emitted from an internal combustion engine such as a diesel engine, thereby purifying the exhaust gas.

[0002] Because NOx and PM contained in diesel engine exhaust gases can be released into the atmosphere and have adverse effects on humans and the environment, a honeycomb structure carrying a NOx catalyst and a ceramic honeycomb filter for capturing PM have traditionally been installed in the exhaust pipe of diesel engines as exhaust systems. An example of a ceramic honeycomb filter for capturing PM in exhaust gases and purifying them is shown in Figures 1(a) and 1(b). The ceramic honeycomb filter 100 comprises a ceramic honeycomb structure 110 consisting of porous partition walls 12 and an outer wall 11 that form a plurality of flow channels 13 and 14, and inlet-side plugging portions 16a and outlet-side plugging portions 16b that alternately plug the exhaust gas inlet-side end faces 15a and exhaust gas outlet-side end faces 15b of the flow channels 13 and 14 in a checkerboard pattern. As shown by the dotted arrows in FIG. 1( b ), exhaust gas flows into the outlet-side sealed flow passages 13 that open to the exhaust gas inlet-side end face 15 a, passes through the communicating holes present on the surface and inside of the partition walls 12, passes through the inlet-side sealed flow passages 14 that open to the outlet-side end face 15 b, and is discharged from the outlet-side end face 15 b. As the exhaust gas passes through the communicating holes present on the surface and inside of the partition walls 12, PM in the exhaust gas is captured, purifying the exhaust gas. When the captured PM reaches a predetermined accumulation amount, it is combusted, and the ceramic honeycomb filter 100 is regenerated. Because such ceramic honeycomb filters 100 are used in increasingly harsh environments, refractory particles such as silicon carbide (SiC) particles, which have excellent thermal shock resistance, have begun to be used as a constituent material for the ceramic honeycomb structure 110.

[0003] Patent Document 1 discloses a method for inexpensively manufacturing honeycomb structures with high porosity and thermal conductivity at relatively low firing temperatures. The method involves kneading silicon carbide particles and metallic silicon particles with an organic binder to form a clay into a honeycomb shape, calcining the resulting molded body to remove the organic binder, and then firing the honeycomb body. Patent Document 1 describes the following: (a) calcining the honeycomb molded body by maintaining it at a predetermined temperature of approximately 150 to 700°C or by increasing the temperature at a rate of 50°C / hr or less within a predetermined temperature range; and (b) firing the honeycomb body at a temperature range of 1400 to 1600°C, preferably in a non-oxidizing atmosphere such as N2 or Ar above the temperature at which oxidation begins. However, firing in a non-oxidizing atmosphere requires expensive equipment, which increases production costs.

[0004] Patent Document 2 discloses a method for producing a porous material comprising aggregate particles made of silicon carbide particles or silicon nitride particles having an oxide film containing cristobalite formed on the surface thereof, cordierite, and a binder that bonds the aggregate particles together while forming pores, by molding a mixture of an aggregate raw material containing silicon carbide particles or silicon nitride particles, a binder raw material containing 35 to 45% by mass of talc, 45 to 60% by mass of aluminum oxide, and 0 to 10% by mass of silicon dioxide, and a pore-forming material, calcining the resulting molded body in an air atmosphere at 200 to 600°C, firing the resulting calcined body in a non-oxidizing atmosphere at 1300°C or higher, and oxidizing the resulting fired body in an oxidizing atmosphere at 1100°C or higher.

[0005] Patent Document 3 discloses a method for producing a porous material in which the silicon carbide aggregates are bound together by the oxide ceramics while maintaining a plurality of pores, and an oxygen-containing phase is formed on the surface of the aggregate (including the interface with the binder), by forming a kneaded product of an aggregate powder made of silicon carbide, a binder raw material including a cordierite-forming raw material, and an organic binder, calcining the resulting molded body in an oxygen-containing atmosphere to remove the organic binder, and then performing a main firing at a temperature range of 1370 to 1450°C to produce a porous fired body in which the aggregate powders are bound together by the oxide ceramics, and then heat-treating the resulting fired body in an oxygen-containing atmosphere at a temperature range of 1000 to 1400°C, thereby producing a porous material in which the silicon carbide aggregates are bound together by the oxide ceramics while maintaining a plurality of pores, and an oxygen-containing phase is formed on the surface of the aggregate (including the interface with the binder).

[0006] However, in the methods for producing porous materials described in Patent Documents 2 and 3, after calcination, firing is performed in an inert atmosphere, and then heat treatment is performed in an oxidizing atmosphere. This not only increases the cost of using an expensive inert atmosphere, but also requires expensive equipment for firing in an inert atmosphere, and also requires an oxidation treatment furnace, resulting in high costs.

[0007] In view of these circumstances, the present applicant previously disclosed a method for producing a silicon carbide ceramic honeycomb structure by kneading silicon carbide particles, a binder containing alumina source particles and magnesia source particles, and an organic binder to obtain a clay, extruding the resulting molded body into a honeycomb shape, drying the resulting molded body, and then firing it in an air atmosphere at a temperature in the range of 1200 to 1350° C. (Patent Document 4). This method not only performs firing in a non-oxidizing atmosphere at a lower temperature than conventional methods, but also does not require pre-firing or post-firing heat treatment, making it possible to produce a silicon carbide ceramic honeycomb structure more inexpensively than conventional methods.

[0008] However, there is a demand for a ceramic honeycomb structure to be used in a ceramic honeycomb filter that not only has higher thermal shock resistance than conventional structures, but also can be manufactured more inexpensively than conventional structures.

[0009] Japanese Patent Publication No. 2002-201082 Japanese Patent Publication No. 2019-167278 Japanese Patent Publication No. 2017-178721 International Publication No. 2022 / 202903 Object of the invention

[0010] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a silicon carbide ceramic honeycomb structure which not only has higher thermal shock resistance than conventional structures but can also be manufactured more inexpensively than conventional structures.

[0011] In order to achieve the above object, the present inventors have conducted extensive research into means for obtaining a silicon carbide ceramic honeycomb structure having higher thermal shock resistance than conventional ceramic honeycomb structures, even when using a firing process that uses a lower firing temperature than conventional ceramic honeycomb structures and does not require a non-oxidizing atmosphere, and have arrived at the present invention.

[0012] That is, the silicon carbide ceramic honeycomb structure of the present invention has a plurality of flow paths separated by porous partition walls so as to penetrate from a first end face to a second end face, the partition walls having aggregates made of silicon carbide, SiO layers present on the surfaces of the aggregates, and a binder phase containing a cordierite phase and a spinel phase, the aggregates having portions bonded to each other by the SiO layers without the binder phase and portions bonded to each other by the SiO layers via the binder phase, the SiO layers having an amorphous SiO phase and a crystalline SiO phase, and a 49×10 -7 It is characterized by a thermal expansion coefficient of 1000kJ / °C or less (between room temperature and 800°C).

[0013] The spinel phase preferably has an amorphous spinel phase and a crystalline spinel phase, and the mass ratio of the amorphous spinel phase to the crystalline spinel phase is preferably 3 or more.

[0014] The mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase in the SiO2 layer is preferably 3 or more.

[0015] It is preferable that the ratio (t1 / t2) of the thickness t1 of the SiO2 layer at the portion where the aggregates are bonded together by the SiO2 layer without the binder phase to the thickness t2 of the SiO2 layer at the portion where the aggregates are bonded together by the SiO2 layer via the binder phase is greater than 1 (t1 > t2).

[0016] The molar ratio M1 of the cordierite phase [=number of moles of cordierite phase / (number of moles of cordierite phase+number of moles of spinel phase)] is preferably 0.20 to 0.90, and more preferably 0.45 to 0.90.

[0017] The total content of the cordierite phase and the spinel phase in the binder phase is preferably 35 mass % or more.

[0018] A preferred silicon carbide ceramic honeycomb structure of the present invention has porous partition walls forming a plurality of flow paths penetrating from a first end face to a second end face, and an outer peripheral wall, wherein the partition walls have aggregates made of silicon carbide, an SiO2 layer present on the surface of the aggregate, and a binder phase containing a cordierite phase and a spinel phase, wherein the spinel phase has an amorphous spinel phase and a crystalline spinel phase, and the mass ratio of the amorphous spinel phase to the crystalline spinel phase in the spinel phase is 3 or more, the aggregates have portions bonded by the SiO2 layer without the binder phase and portions bonded by the SiO2 layer via the binder phase, the SiO2 layer has an amorphous SiO2 phase and a crystalline SiO2 phase, and the mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase in the SiO2 layer is 3 or more, a molar ratio M1 of the cordierite phase in the binder phase [=number of moles of cordierite phase / (number of moles of cordierite phase+number of moles of spinel phase)] of 0.2 or more, and a thermal expansion coefficient (between room temperature and 800°C) of the silicon carbide ceramic honeycomb structure of 49×10 -7 / °C or less.

[0019] It is preferable that the flow path comprises first and second flow paths arranged alternately in the horizontal direction, the first flow path opens at the first end face and has a plugging portion at the second end face, and the second flow path has a plugging portion at the first end face and opens at the second end face.

[0020] In the cross section in the lateral direction (cross section perpendicular to the flow direction), the cross-sectional area of ​​the first flow path is preferably larger than the cross-sectional area of ​​the second flow path.

[0021] The bonded ceramic honeycomb segments of the present invention are formed by bonding the outer peripheral wall surfaces of a plurality of honeycomb segments together, and each of the honeycomb segments is made of the silicon carbide ceramic honeycomb structure.

[0022] According to the present invention, by firing at a lower temperature than conventionally possible without requiring a non-oxidizing atmosphere, and in particular by performing a firing process in an air atmosphere that includes a first holding step in which the temperature is maintained at a relatively low range of 1100 to 1200°C and a second holding step in which the temperature is maintained at a range of 1250 to 1350°C, it is possible to produce a silicon carbide ceramic honeycomb structure having higher thermal shock resistance than conventionally possible at a lower cost than conventionally possible.

[0023] FIG. 6 is a front view schematically showing an example of a ceramic honeycomb structure constituting an integral ceramic honeycomb filter. FIG. 7 is a longitudinal cross-sectional view schematically showing an example of a ceramic honeycomb structure constituting an integral ceramic honeycomb filter. FIG. 8 is a perspective view schematically showing an example of a ceramic honeycomb segment constituting a segment-bonded ceramic honeycomb filter. FIG. 9 is a perspective view schematically showing an example of a segment-bonded ceramic honeycomb filter. FIG. 10 is a perspective view schematically showing another example of a ceramic honeycomb segment. FIG. 11 is a partially enlarged cross-sectional view schematically showing the bonding state between the aggregate and the binder phase in the partition walls of the silicon carbide ceramic honeycomb structure of the present invention. FIG. 12 is a secondary electron image by EPMA (magnification: 500 times) of a sample cut out from the partition walls of the silicon carbide ceramic honeycomb structure of Example 1. FIG. 13 is a diagram showing each phase obtained by elemental mapping of FIG.

[0024] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, but the present invention is not limited thereto, and various changes, modifications, or improvements can be made without departing from the technical spirit of the invention.

[0025] [1] Silicon carbide ceramic honeycomb structure The silicon carbide ceramic honeycomb structure of the present invention has porous partition walls that form a plurality of flow paths that penetrate from a first end face to a second end face, and an outer wall, and the partition walls have aggregates made of silicon carbide, an SiO2 layer present on the surface of the aggregate, and a binder phase containing a cordierite phase and a spinel phase, and the aggregates have portions where they are bonded by the SiO2 layer without the binder phase and portions where they are bonded by the SiO2 layer via the binder phase, the SiO2 layer has an amorphous SiO2 phase and a crystalline SiO2 phase, and the thermal expansion coefficient of the silicon carbide ceramic honeycomb structure (between room temperature and 800°C) is 49 × 10 -7 / ° C. or less. The silicon carbide ceramic honeycomb structure of the present invention is basically made of a porous composite material composed of silicon carbide aggregate particles and an oxide ceramic binder.

[0026] (1) Aggregate The aggregate, which is one of the materials constituting the partition walls, is a particle made of silicon carbide and has an SiO2 layer on its surface. The aggregates have portions bonded by the SiO2 layer without a binder phase and portions bonded by the SiO2 layer via a binder phase, and the SiO2 layer has an amorphous SiO2 phase and a crystalline SiO2 phase. The amorphous SiO2 phase, which has a small thermal expansion coefficient, suppresses the thermal expansion of the SiO2 layer, so the ceramic honeycomb structure of the present invention has a low thermal expansion coefficient and good thermal shock resistance.

[0027] When the mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase in the SiO2 layer is 3 or more, the proportion of the amorphous SiO2 phase, which has a small thermal expansion coefficient, is sufficiently high, so that the thermal expansion of the SiO2 layer can be further reduced, and the thermal shock resistance of the ceramic honeycomb structure can be improved.The mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase in the SiO2 layer is more preferably 3.1 to 7.5.

[0028] The ratio (t1 / t2) of the thickness t1 of the SiO2 layer at the portion where aggregates are bonded without a binder phase to the thickness t2 of the SiO2 layer at the portion where aggregates are bonded via a binder phase is preferably greater than 1 (t1>t2). When t1>t2, the aggregates are bonded largely by the amorphous SiO2 phase, which has a small thermal expansion coefficient, and the thermal expansion of the ceramic honeycomb structure is kept small and the thermal shock resistance is improved. It is more preferable that t1 / t2 is 2.0 to 3.5.

[0029] The thickness t1 of the SiO2 layer at the site where aggregates are bonded without a binder phase and the thickness t2 of the SiO2 layer at the site where aggregates are bonded via a binder phase can be measured by the following method. The cut surface of a test piece cut from a ceramic honeycomb structure is polished, and six randomly selected fields (longer side 256 μm, shorter side 192 μm) are subjected to mapping analysis using an electron probe microanalyzer (EPMA) at 500x magnification. After mapping the four elements O, Si, Al, and Mg for each field, the images are overlaid to obtain five color-coded analytical photographs: Si, Si + O, Mg + Si + O, Al + Mg + O, and Al + Mg + Si + O. Ten lines are drawn at equal intervals in both the horizontal and vertical directions on each analytical photograph. The length of each line passing through the SiO2 layer at the site where aggregates are bonded without a binder phase is measured, and the sum of the measured lengths of all horizontal and vertical lines is divided by the number of measurement sites to obtain the average value, which is used to calculate t1. ’ Similarly, the length of each straight line passing through the SiO2 layer at the portion where the aggregates are bonded together via the binder phase is measured, and the sum of the measured lengths of all the straight lines in the horizontal and vertical directions is divided by the number of measurement portions to obtain the average value, and t2 ’ This procedure is carried out for all six fields of view of the same test piece, and t1 ’ and t2 ’ The average values ​​are calculated and used as t1 and t2 of the test piece.

[0030] (2) Binder Phase The binder phase has a cordierite phase and a spinel phase. In addition to the cordierite phase and the spinel phase, the binder phase may also contain at least one crystalline or amorphous phase selected from the group consisting of cristobalite, mullite, forsterite, protoenstatite, alumina (corundum), and magnesia (periclase).

[0031] The spinel phase preferably contains both an amorphous spinel phase and a crystalline spinel phase. The amorphous spinel phase, which has a small thermal expansion coefficient, can suppress the thermal expansion of the binder phase, improving the thermal shock resistance of the ceramic honeycomb structure. Note that, since the strength decreases when the spinel phase is only amorphous spinel, it is preferable that the spinel phase also contains crystalline spinel.

[0032] The mass ratio of the amorphous spinel phase to the crystalline spinel phase in the binder phase is preferably 3 or more. This increases the proportion of the amorphous spinel phase, which has a small thermal expansion coefficient, in the binder phase, making it possible to further reduce the thermal expansion of the binder phase and improve thermal shock resistance. The mass ratio of the amorphous spinel phase to the crystalline spinel phase is more preferably 3.1 to 7.5.

[0033] In order to sufficiently increase the strength and thermal shock resistance of the binder phase that binds the aggregates, the molar ratio M1 of the cordierite phase in the binder phase is preferably 0.2 or more, more preferably 0.45 to 0.90. The molar ratio M1 of the cordierite phase is calculated by dividing the number of moles of the cordierite phase by (the number of moles of the cordierite phase + the number of moles of the spinel phase). If the molar ratio M1 of the cordierite phase is less than 0.2, the strength of the binder phase decreases and the thermal expansion coefficient increases, resulting in a deterioration in the thermal shock resistance of the ceramic honeycomb structure. Note that if the molar ratio M1 of the cordierite phase exceeds 0.90, the heat resistance of the binder phase decreases and the porosity of the partition walls decreases. The lower limit of the molar ratio M1 is more preferably 0.47, even more preferably 0.50, and most preferably 0.55. On the other hand, the upper limit of the molar ratio M1 is more preferably 0.89, even more preferably 0.85, and most preferably 0.83.

[0034] In order for the binder phase to have sufficient strength and thermal shock resistance, the total content of the cordierite phase and the spinel phase in the binder phase is preferably 35% by mass or more, more preferably 38% by mass or more, and most preferably 40% by mass or more. The upper limit of the total content of the cordierite phase and the spinel phase is not particularly limited, but may be 80% by mass or less, for example, 75% by mass or less.

[0035] The molar ratio M1 of the cordierite phase can be determined by the following method. A portion of the fired silicon carbide ceramic honeycomb structure is powdered and measured by X-ray diffraction (hereinafter referred to as XRD or powder X-ray diffraction). From the obtained powder diffraction chart, the peak intensity of the cordierite (110) plane, the peak intensity of the spinel (311) plane, the peak intensity of the SiO2 cristobalite (101) plane, the peak intensity of the mullite (110) plane, and the peak intensity of the forsterite (130) plane are measured, and the mass ratios of the cordierite, spinel, cristobalite, mullite, and forsterite crystalline phases in the entire binder phase are calculated. The masses per mole of cordierite and spinel are set to 585.0 and 142.3, respectively, and the number of moles of cordierite and spinel is calculated from the obtained mass ratios. The molar ratio M1 of the cordierite phase is calculated from the number of moles of the cordierite phase and the number of moles of the spinel phase by the formula: number of moles of cordierite phase / (number of moles of cordierite phase+number of moles of spinel phase).

[0036] The total content of the cordierite phase and the spinel phase in the binder phase is determined from the mass ratios of the cordierite phase, the spinel phase, the cristobalite phase, the mullite phase, and the forsterite phase determined by the above method, by the formula: (total mass ratios of the cordierite phase and the spinel phase) / (total mass ratios of the cordierite phase, the spinel phase, the cristobalite phase, the mullite phase, and the forsterite phase).

[0037] The mass ratios of the amorphous SiO2 phase to the crystalline SiO2 phase and the mass ratios of the amorphous spinel phase to the crystalline spinel phase are determined using a combination of powder X-ray diffraction and EPMA analysis. Specifically, the crystalline SiO2 phase fraction Wc (mass%) is determined by XRD, and the SiO2 phase fraction W (mass%), which is the sum of amorphous and crystalline SiO2, is determined by EPMA. The amorphous SiO2 fraction Wa (mass%) is then calculated by subtracting Wc from W. The mass ratio Wa / Wc of the amorphous SiO2 phase to the crystalline SiO2 phase is calculated by dividing the amorphous SiO2 fraction Wa (mass%) by the crystalline SiO2 fraction Wc (mass%). The mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase can also be calculated using a similar method.

[0038] The silicon carbide ceramic honeycomb structure of the present invention having the above structure has a size of 49×10 -7 / °C or less (between room temperature and 800°C). The thermal expansion coefficient is preferably 48 x 10 -7 / °C or less, and more preferably 47 × 10 -7 / ℃ or less.

[0039] The silicon carbide ceramic honeycomb structure of the present invention having the above structure has a maximum bending stress exceeding 4.0 MPa, preferably 4.5 MPa or more, and more preferably 5.0 MPa or more.

[0040] The silicon carbide ceramic honeycomb structure of the present invention having the above structure has a thermal shock fracture resistance R, calculated from R = σ(1 - ν) / αE, where σ is the maximum bending stress, E is the Young's modulus, α is the thermal expansion coefficient, and ν is the Poisson's ratio, in the range of 350 to 700°C. The lower limit of the thermal shock fracture resistance is preferably 380°C, more preferably 400°C, and the upper limit is preferably 680°C, more preferably 660°C.

[0041] (3) Structure As shown in Figures 1(a) and 1(b), a silicon carbide ceramic honeycomb structure 110 according to one embodiment of the present invention has partition walls 12 that define first and second flow paths 13, 14, and an outer peripheral wall 11 formed on its outer peripheral surface, thereby constituting an integral ceramic honeycomb filter 100. The first flow paths 13 open to a first end face 15a on the exhaust gas inlet side and have plugging portions 16b on a second end face 15b on the exhaust gas outlet side, while the second flow paths 14 have plugging portions 16a on the first end face 15a and open to the second end face 15b. The plugging portions 16a, 16b are alternately arranged in a checkerboard pattern on each end face 15a, 15b.

[0042] The silicon carbide ceramic honeycomb filter 200 shown in Fig. 3 is obtained by using a silicon carbide ceramic honeycomb structure according to another embodiment of the present invention shown in Fig. 2 as honeycomb segments 211 and integrally bonding the peripheral wall surfaces of a plurality of honeycomb segments 211 together via a bonding material layer 29. Each ceramic honeycomb segment 211 has partition walls 22 that define first and second flow paths 23, 24, and an outer peripheral wall 21 is formed on its outer peripheral surface. The first flow path 23 opens to a first end face 25a on the exhaust gas inlet side and has plugging portions 26b on a second end face 25b on the exhaust gas outlet side. The second flow path 24 has plugging portions 26a on the first end face 25a and opens to the second end face 25b. The plugging portions 26a, 26b are alternately arranged in a checkerboard pattern on each end face 25a, 25b.

[0043] The plugging portions 16a, 16b, 26a, and 26b may be formed on either the honeycomb formed body before firing or the honeycomb structure after firing. The plugging portions 16a, 16b, 26a, and 26b may be formed so as to contact the end faces 15a, 15b, 25a, and 25b, respectively, or may be formed at positions inward from the end faces 15a, 15b, 25a, and 25b, respectively.

[0044] As shown in Figure 4, in a horizontal cross section (cross section perpendicular to the flow direction of exhaust gas) of a silicon carbide ceramic honeycomb segment 311, the cross-sectional area of ​​the first flow path (outlet-side sealed flow path) 33 may be larger than the cross-sectional area of ​​the second flow path (inlet-side sealed flow path) 34.

[0045] The cross-sectional shape of the first and second flow paths in the horizontal direction can be a polygonal shape such as a triangle, a rectangle, a hexagon, or an octagon, or a polygon with arc-shaped vertices. The cross-sectional shapes of the first and second flow paths can be the same or different.

[0046] In order to have good thermal shock resistance, the thickness of the partition walls of the silicon carbide ceramic honeycomb structure of the present invention is preferably 150 to 280 μm.

[0047] In order to maintain low pressure loss and high strength, the porosity of the partition walls of the silicon carbide ceramic honeycomb structure of the present invention is preferably 30 to 50%. If the porosity is less than 30%, the pressure loss of the ceramic honeycomb structure will be large, and if it exceeds 50%, sufficient strength will not be obtained. The lower limit of the porosity is more preferably 35%, and most preferably 37%. The upper limit of the porosity is more preferably 48%, and most preferably 46%.

[0048] In order to maintain high strength, the median pore diameter of the partition walls of the silicon carbide ceramic honeycomb structure of the present invention is preferably 3 to 20 μm. If the median pore diameter is less than 3 μm, the pressure loss of the ceramic honeycomb structure increases, and if it exceeds 20 μm, sufficient strength cannot be obtained. The lower limit of the median pore diameter is more preferably 5 μm, and most preferably 7 μm. The upper limit of the median pore diameter is more preferably 18 μm, and most preferably 16 μm.

[0049] The porosity and median pore diameter of the partition walls can be measured by mercury intrusion porosimetry. A test piece (10 mm × 10 mm × 10 mm) cut out from a ceramic honeycomb structure is placed in a measurement cell of an Autopore III manufactured by Micromeritics. After the pressure inside the cell is reduced, mercury is introduced to apply pressure, and the relationship between the pressure at the time of pressurization and the volume of mercury forced into the pores present in the test piece is determined. The pressure is converted into pore diameter, and the cumulative pore volume (equivalent to the volume of mercury) integrated from the larger pore diameter side to the smaller pore diameter side is plotted against the pore diameter to obtain a graph showing the relationship between pore diameter and cumulative pore volume. The pressure for introducing mercury is 0.5 psi (0.35 × 10 -3 kg / mm2 ) and the contact angle = 130° and surface tension = 484 dyne / cm are used as constants when calculating the pore diameter from the pressure. 2 The cumulative pore volume in the pores (corresponding to a pore diameter of approximately 0.1 μm) is defined as the total pore volume V (cm 3 The porosity P (volume %) is calculated from the measured value of the total pore volume V by P = ρV / (1 + ρV) × 100 [where ρ is the true specific gravity of silicon carbide (= 3.2 g / cm 3 The median pore diameter is the pore diameter when the cumulative pore volume is 50% of the total pore volume in a graph showing the relationship between pore diameter and cumulative pore volume.

[0050] After bonding the plurality of honeycomb segments 211 together with the bonding material layer 29, the outer periphery of the ceramic honeycomb segment bonded body 210 is processed so that the outer peripheral shape of the cross section in the horizontal direction becomes a circle, an ellipse, a triangle, a rectangle, or the like, and the processed outer peripheral surface is covered with a coating material to form the outer peripheral wall 21.

[0051] [2] Manufacturing Method of Silicon Carbide Ceramic Honeycomb Structure The silicon carbide ceramic honeycomb structure of the present invention can be manufactured, for example, by the following method. First, silicon carbide particles as aggregate, binder phase raw material powder including alumina source particles and magnesia source particles, and an organic binder are mixed. In addition to the alumina source particles and magnesia source particles, the binder phase raw material powder may also include spinel particles, mullite particles, forsterite particles, etc., containing the alumina source and the magnesia source.

[0052] The alumina source particles are particles of a compound containing alumina (AlO) or particles of a compound containing alumina (AlO) and magnesia (MgO). Specifically, the alumina source particles are preferably alumina particles or aluminum hydroxide particles.

[0053] The magnesia source particles are particles of a compound containing magnesia (MgO) or particles of a compound containing alumina (Al2O3) and magnesia (MgO). Specifically, the magnesia source particles are preferably magnesium oxide particles, magnesium hydroxide particles, or talc particles.

[0054] By using alumina particles or aluminum hydroxide particles as the alumina source particles and one or more of magnesium oxide particles, magnesium hydroxide particles, and talc particles as the magnesia source particles, it becomes possible to perform firing at a lower temperature than conventionally possible without requiring a non-oxidizing atmosphere.

[0055] In order to obtain a binder phase containing a cordierite phase and a spinel phase, the molar ratio M2 of the alumina source particles in the binder phase raw material powder [= number of moles of (Al2O3) / (number of moles of (Al2O3)+number of moles of (MgO)] is preferably 0.32 to 0.50. The molar ratio M2 can be determined by calculating the number of moles of alumina (Al2O3) and magnesia (MgO) from the masses of the blended alumina source particles and magnesia source particles, and dividing the number of moles of alumina (Al2O3) by the total number of moles of alumina (Al2O3) and magnesia (MgO).

[0056] For example, aluminum hydroxide [Al(OH)3] is used as the alumina source, magnesium hydroxide [Mg(OH)2] or talc [Mg3SiO4O 10 (OH)2], the alumina content in aluminum hydroxide and the magnesia content in magnesium hydroxide and talc are respectively: Al(OH)3 = (1 / 2)Al2O3 + (3 / 2)H2O Mg(OH)2 = MgO + H2O Mg3SiO 10 Since the formula is (OH)2 = 3MgO + 4SiO2 + H2O, we can calculate that the alumina content per mole of aluminum hydroxide is 0.5 moles, the magnesia content in 1 mole of magnesium hydroxide is 1 mole, and the magnesia content in 1 mole of talc is 3 moles. Using this relationship, we can determine the number of moles of alumina and magnesia, and then calculate the molar ratio M2. Similarly, when using particles of a compound containing both alumina and magnesia (for example, spinel), we calculate the alumina (Al2O3) and magnesia (MgO) content in this compound to determine the molar ratio M2.

[0057] If the molar ratio M2 is less than 0.32 or more than 0.50, the thermal shock resistance decreases. The lower limit of the molar ratio M2 is more preferably 0.35, and most preferably 0.40. The upper limit of the molar ratio M2 is more preferably 0.48.

[0058] The binder phase raw material powder used in the manufacture of the silicon carbide ceramic honeycomb structure of the present invention is an oxide ceramic composed of alumina source particles and magnesia source particles, and is not metallic silicon as used in the prior art. Therefore, the firing in a non-oxidizing atmosphere and subsequent oxidation treatment that were previously required to bond metallic silicon are not required. This makes it possible to reduce the cost required for firing, and enables the manufacture of ceramic honeycomb structures at lower cost than the prior art.

[0059] The total amount of the alumina source particles and magnesia source particles relative to 100% by mass of the silicon carbide particles is preferably 5 to 20% by mass. If it is less than 5% by mass, the bonding strength of the binder phase decreases, resulting in a decrease in the strength of the ceramic honeycomb structure. On the other hand, if it exceeds 20% by mass, the thermal shock resistance of the ceramic honeycomb structure decreases. The lower limit of the total amount of the alumina source particles and magnesia source particles relative to 100% by mass of the silicon carbide particles is more preferably 6% by mass, and most preferably 7% by mass. Furthermore, the upper limit of the total amount of the alumina source particles and magnesia source particles is preferably 19% by mass, and most preferably 18% by mass.

[0060] The silicon carbide particles preferably have an average particle size of 20 to 50 μm, and the alumina source particles and magnesia source particles each preferably have an average particle size of 1 to 15 μm.

[0061] To obtain a ceramic honeycomb structure having good porosity and median pore size, the median particle size D50 of the ceramic particles including the silicon carbide particles and the binder phase raw material powder is preferably 15 to 45 μm. The lower limit of D50 is more preferably 18 μm, and most preferably 20 μm. The upper limit of D50 is more preferably 40 μm, and most preferably 35 μm.

[0062] In manufacturing the silicon carbide ceramic honeycomb structure of the present invention, it is preferable to add only an organic binder with a small pore-forming effect without adding a pore-forming material (such as graphite particles, expanded resin particles, expanded resin particles, water-absorbent resin particles, starch, or silica gel particles). Examples of organic binders include methyl cellulose, ethyl cellulose, ethyl methyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl ethyl cellulose. Among these, hydroxypropyl methyl cellulose or methyl cellulose is preferred. The amount of organic binder added is preferably 5 to 15% by mass relative to 100% by mass of the forming raw material.

[0063] Water is added to the mixed raw materials and kneaded to form a plastic body. To obtain a body with a moldable hardness, the amount of water added is preferably 20 to 50% by mass of the molding raw materials.

[0064] The resulting clay is extruded from a honeycomb structure molding die by a known method to form a honeycomb structure molded body. After drying this molded body, the end faces and periphery are processed as necessary, and then fired to obtain a silicon carbide ceramic honeycomb structure. The drying method is not particularly limited, but preferred methods include hot air drying, microwave heating drying, and high-frequency heating drying.

[0065] The firing in the air atmosphere preferably comprises a first holding step of holding the mixture at a first temperature range of 1100 to 1200°C for 0.5 to 5 hours, and a second holding step of holding the mixture at a second temperature range of 1250 to 1350°C for 0.5 to 5 hours. This promotes the synthesis of a spinel phase (MgO.Al2O3) (crystalline spinel phase and amorphous spinel phase) from the alumina source and magnesia source, and also produces an SiO2 layer (composed of crystalline SiO2 phase and amorphous SiO2 phase) on the surface of the silicon carbide particles by oxidation.

[0066] The amorphous SiO2 phase, which has a thermal expansion coefficient much smaller than that of the crystalline SiO2 phase, can suppress the thermal expansion of the SiO2 layer. Furthermore, the amorphous spinel phase in the binder phase and the amorphous SiO2 phase in the SiO2 layer synthesize cordierite at a temperature lower than the usual cordierite synthesis temperature. Because the binder phase thus generated has a small thermal expansion coefficient, silicon carbide ceramic honeycomb structures with thermal shock resistance equal to or greater than conventional structures can be obtained at lower cost than conventional structures.

[0067] If the temperature range of the first holding step is less than 1100°C, the synthesis of the spinel phase is not promoted, and it becomes difficult to synthesize cordierite in the binder phase. On the other hand, if the temperature exceeds 1200°C, the formation of the crystalline SiO2 phase in the SiO2 layer is promoted, making it difficult to keep the thermal expansion of the SiO2 layer small and increasing the thermal expansion coefficient of the synthesized cordierite.

[0068] If the temperature range of the second holding step is less than 1250°C, it becomes difficult to generate an amorphous SiO2 phase in the SiO2 layer, making it difficult to keep the thermal expansion of the SiO2 layer small, and the thermal expansion coefficient of the synthesized cordierite becomes large. On the other hand, if the temperature exceeds 1350°C, the firing temperature becomes too high, making it difficult to keep the firing cost lower than before.

[0069] In contrast, if the second holding step is not performed, (a) if the firing temperature is high, not only is the ratio of the amorphous SiO2 phase to the crystalline SiO2 phase small, but also the ratio of the thickness t1 of the SiO2 layer at the portion where the aggregate made of silicon carbide is bonded without a binder phase to the thickness t2 of the SiO2 layer at the portion where it is bonded via a binder phase is small; and (b) if the firing temperature is low, not only is the formation of the SiO2 layer insufficient, but the molar ratio M1 of the cordierite phase in the binder phase is also small, resulting in the problem that the thermal expansion coefficient (between room temperature and 800°C) of the obtained silicon carbide ceramic honeycomb structure becomes too large.

[0070] In the fired silicon carbide ceramic honeycomb structure, plugging portions are formed at the openings on the second end face side of the first flow passages and the openings on the first end face side of the second flow passages. A slurry containing silicon carbide particles is preferably used as the plugging material. The plugging portions may be formed before firing the silicon carbide ceramic honeycomb structure.

[0071] A bonding material is applied to the outer peripheral wall surface of each honeycomb segment 211 made of a silicon carbide ceramic honeycomb structure having plugged portions formed therein, and the outer peripheral wall surfaces of the plurality of honeycomb segments 211 are bonded together with a bonding material layer 29 as shown in Fig. 3 to form a bonded silicon carbide ceramic honeycomb segment assembly 210. The bonding material is preferably a paste made of silicon carbide particles and colloidal silica.

[0072] After drying, the ceramic honeycomb segment bonded body 210 is fired at a temperature range of 1000 to 1400°C. The outer periphery of the fired silicon carbide ceramic honeycomb segment bonded body 210 is machined into a circular shape using a lathe. Next, the circular outer periphery is coated with an outer skin material made of silicon carbide particles and inorganic particles (colloidal silica) to form an outer wall, and then dried to obtain the silicon carbide ceramic honeycomb filter 200.

[0073] The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[0074] Example 1: 100% by mass of silicon carbide particles (D50: 29.3 μm) serving as aggregate was mixed with 17.4% by mass of a binder phase raw material powder consisting of aluminum hydroxide particles, magnesium hydroxide particles, and talc particles, so that the alumina molar ratio M2 [(Al2O3) / (Al2O3 + MgO)] was 0.45, resulting in a mixture powder with a median diameter of 24.8 μm. Hydroxypropyl methylcellulose was then added as an organic binder to this mixture, followed by addition of water and kneading to form a plastic puddle. The puddle was extruded from a honeycomb structure molding die in a screw molding machine to obtain a honeycomb molded body with a rectangular outer shape with sides of 34 mm and a length of 304 mm. This honeycomb formed body was dried in a hot air dryer at 120°C for 2 hours, and then fired under the conditions shown in Table 1, including the first and second holding steps, to produce a honeycomb formed body with a partition wall thickness of 8 mil (0.20 mm) and a cell density of 300 cpsi (46.5 cells / cm). 2 A silicon carbide ceramic honeycomb structure having the above-mentioned structure was obtained.

[0075] FIG. 6 shows a secondary electron image (magnification: 500x) of a sample cut from a partition wall of the silicon carbide ceramic honeycomb structure of Example 1. Furthermore, in the same field of view as FIG. 6, four elements (O, Si, Al, and Mg) were mapped by EPMA, and then overlapped to divide the image into four regions: Si, Si + O, Al + Mg + O, and Al + Mg + Si + O. Each region is shown in FIG. 7. In FIG. 7, (a) shows the Si region corresponding to the silicon carbide aggregate 1, (b) shows the Si + O region corresponding to the SiO layer 3, (c) shows the binder phase 2, (d) shows the Al + Mg + O region corresponding to the spinel phase 4, and (e) shows the Al + Mg + Si + O region corresponding to the cordierite phase 5. The proportion of the cordierite phase can be calculated by subtracting the proportion of the spinel phase 4 from the proportion of the binder phase 2.

[0076] From Figures 6 and 7, it was found that the partition walls of the silicon carbide ceramic honeycomb structure of Example 1 have aggregate 1 and binder phase 2, that an SiO2 layer 3 is present on the surface of aggregate 1, and that binder phase 2 contains cordierite phase and spinel phase 4.

[0077] Examples 2 to 6: The same procedures as in Example 1 were carried out except that the firing conditions including the first and second holding steps were changed as shown in Table 1, and the partition wall thickness was 8 mil (0.20 mm) and the cell density was 300 cpsi (46.5 cells / cm). 2 Observation by EPMA confirmed that each of the silicon carbide ceramic honeycomb structures had a microstructure similar to that of Example 1, that the partition walls of the silicon carbide ceramic honeycomb structures had an aggregate 1 and a binder phase 2, that an SiO2 layer 3 was present on the surface of the aggregate 1, and that the binder phase 2 contained a cordierite phase and a spinel phase.

[0078] Comparative Example 1: 100% by mass of silicon carbide particles (D50: 38.4 μm) serving as aggregate was blended with 25.0% by mass of metallic silicon particles (D50: 11.8 μm) serving as a binder phase to obtain ceramic particles with a median diameter of 32.9 μm. Hydroxypropyl methylcellulose was mixed with the ceramic particles as an organic binder and kneaded with water to form a plastic clay. The clay was extruded from a honeycomb structure molding die in a screw molding machine to obtain a honeycomb molded body with a rectangular outer shape of 34 mm on a side and a length of 304 mm. This honeycomb molded body was dried in a hot air dryer at 120°C for 2 hours, then degreased at 550°C for 3 hours, and then fired at 1450°C in an argon atmosphere for 5 hours to obtain a partition wall thickness of 8 mil (0.20 mm) and a cell density of 300 cpsi (46.5 cells / cm). 2 In Comparative Example 1, in which only metallic silicon particles were used as the raw material for the binder phase, a binder phase consisting of metallic silicon and an SiO2 layer formed by oxidation of Si derived from the raw material metallic silicon particles or silicon carbide particles during firing were observed, covering the silicon carbide particles (aggregate). However, no binder phase 2 containing cordierite and spinel phases was observed. Note that the ratio of crystalline SiO2 to amorphous SiO2 was not measured in Comparative Example 1.

[0079] Comparative Examples 2 and 3: A honeycomb formed body obtained in the same manner as in Example 1 was dried in a hot air dryer at 120°C for 2 hours, and then fired under conditions including only the first holding step as shown in Table 1, to obtain a honeycomb formed body having a partition wall thickness of 8 mil (0.20 mm) and a cell density of 300 cpsi (46.5 cells / cm).2 A silicon carbide ceramic honeycomb structure having the above-mentioned structure was obtained.

[0080] For the silicon carbide ceramic honeycomb structures of Examples 1 to 6 and Comparative Examples 1 to 3, the structure of the SiO layer on the aggregate surface in the partition wall, the thickness t1 of the SiO layer at the portion where aggregates are bonded to each other without a binder phase, the thickness t2 of the SiO layer at the portion where aggregates are bonded to each other via a binder phase, the structure of the binder phase, the mass ratio of the amorphous spinel phase to the crystalline spinel phase in the spinel phase in the binder phase, and the molar ratio M1 of the cordierite phase in the binder phase were measured by the following methods.

[0081] That is, for each of the silicon carbide ceramic honeycomb structures of Examples 1 to 6 and Comparative Examples 1 to 3, the mass ratios of crystalline SiO (cristobalite), spinel, cordierite, and other compounds were determined by XRD, and the molar ratio M of the cordierite phase in the binder phase was calculated using these mass ratios and the mass per mole of each compound. １ The mass % of amorphous SiO2 and crystalline SiO2, and the mass % of amorphous spinel and crystalline spinel in the binder phase were calculated by subtracting the mass % of crystalline compounds determined by XRD from the mass % of each compound (amorphous + crystalline) determined by EPMA. The XRD and EPMA methods are described in detail below. The thicknesses t1 and t2 of the SiO2 layers were measured using the method described in the "(1) Aggregate" section above.

[0082] (i) Identification of compounds and quantification of composition by XRD: Samples taken from each fired honeycomb structure were ground in an alumina mortar to obtain powder with an average particle size of approximately 10 μm. X-ray diffraction measurements of each powder were performed using a fully automated, multipurpose horizontal X-ray diffractometer, SmartLab (Rigaku), under the following conditions: X-ray output: 45 kV, 200 mA, filter: Cu_K-beta, scan range: 8.0000 to 60.0000 deg., step width: 0.0100 deg., and scan speed: 26.9360 deg. / min. In each of the obtained X-ray diffraction charts, the mass ratio of each compound was determined from the height (intensity) of the peaks corresponding to cordierite (plane index (1,1,0), 2θ = 10.4°), SiO2 cristobalite (plane index (1,0,1), 2θ = 21.8°), corundum (plane index (0,1,2), 2θ = 25.6°), spinel (plane index (3,1,1), 2θ = 36.8°), and periclase (plane index (2,0,0), 2θ = 42.8°). The number of moles was calculated from the mass ratio of cordierite and spinel, assuming that the masses of 1 mole of cordierite and spinel are 585.0 and 142.3, respectively, and the molar ratio M1 of the number of moles of cordierite phase to the total number of moles of cordierite phase and the number of moles of spinel phase [= number of moles of cordierite phase / (number of moles of cordierite phase + number of moles of spinel phase)] was determined. All of these compounds identified by XRD were crystalline.

[0083] (ii) Observation of Compound Distribution and Quantification of Composition by EPMA. A 6-cell × 6-cell × 10 mm sample cut from each honeycomb structure was embedded in resin, and the cut surface was polished. EPMA measurements of each polished surface were performed using a field emission electron probe microanalyzer (EPMA) (JEOL XA-8530F) under the following beam irradiation conditions: accelerating voltage: 10.0 kV, beam current: 20 mA, analysis area: 128 μm × 96 μm, measurement pitch: 0.2 μm, and integration time: 0.01 ms / point. The analyzing crystals used for mapping were O: LSA70, Mg: rubidium phthalate (RAP), Al: ammonium dihydrogen phosphate (ADP), and Si: pentaerythritol (PET).

[0084] Mapping of the four elements O, Si, Al, and Mg was performed in six randomly selected fields of view (256 μm × 192 μm) at 500x magnification. Then, overlay processing was performed to obtain five color-coded analytical images: Si, Si + O, Mg + Si + O, Al + Mg + O, and Al + Mg + Si + O. The five color-coded compounds were SiC, SiO2, MgO, spinel, and cordierite, respectively. The mass percentage of each compound was calculated from the area fraction and true density of each compound. Since the calculated mass percentage is the sum of the amorphous and crystalline compounds, subtracting the mass percentage of the crystalline compounds determined by XRD from this calculated mass percentage yields the mass percentage of the amorphous compounds. This method was used to calculate the mass percentages of amorphous SiO2, crystalline SiO2, and amorphous spinel and crystalline spinel in the binder phase.

[0085] (a) Structure of the SiO2 layer The total mass% of amorphous SiO2 and crystalline SiO2 was measured by EPMA, and the mass% of crystalline SiO2 was measured by XRD. Using the above method, it was confirmed that the SiO2 layer formed on the surface of the silicon carbide particles was composed of amorphous SiO2 phase and crystalline SiO2 phase, and the proportions (mass%) of the amorphous SiO2 phase and crystalline SiO2 phase were calculated. The results are shown in Table 2-1.

[0086] (b) Thicknesses t1 and t2 of the SiO2 layer Using the method described in the "(1) Aggregates" section, EPMA mapping analysis was performed on six randomly selected fields of view (long side 256 μm, short side 192 μm) at 500x magnification to determine the thickness t1 of the SiO2 layer at the site where the aggregates were bonded without a binder phase, and the thickness t2 of the SiO2 layer at the site where the aggregates were bonded via a binder phase. The results are shown in Table 2-1.

[0087] (c) Binder Phase Structure: The structure of the binder phase was observed using the powder X-ray diffraction method described in Section "(2) Binder Phase," and it was confirmed that the binder phase contained cordierite and spinel phases. Furthermore, the peak intensity of the cordierite (110) plane, the peak intensity of the spinel (311) plane, the peak intensity of the cristobalite (101) plane, the peak intensity of the mullite (110) plane, and the peak intensity of the forsterite (130) plane were measured, and the mass ratios of the cordierite, spinel, cristobalite, mullite, and forsterite crystalline phases in the entire binder phase were calculated, and the percentage (mass%) of the cordierite phase plus the spinel phase was determined. The results are shown in Table 2-2.

[0088] (d) Mass ratio of amorphous spinel phase to crystalline spinel phase The mass ratio of the amorphous spinel phase to the crystalline spinel phase was determined by the above method, in which the total mass% of the amorphous spinel phase and the crystalline spinel phase was measured by EPMA and the mass% of the crystalline spinel phase was measured by XRD. The results are shown in Table 2-2.

[0089] (e) Molar Ratio M1 of Cordierite Phase The mass percentages of the cordierite phase and spinel phase obtained by the method described in "(i) Quantification of composition by XRD" above were converted to moles, and the molar ratio M1 of the cordierite phase was calculated using the formula: moles of cordierite phase / (moles of cordierite phase+moles of spinel phase). The results are shown in Table 2-2.

[0090] Furthermore, the porosity, median pore size, thermal expansion coefficient, and thermal shock fracture resistance coefficient R of each silicon carbide ceramic honeycomb structure were measured by the following methods.

[0091] (f) Measurement of Porosity and Median Pore Diameter The porosity and median pore diameter were measured by the mercury intrusion method described below. First, a test piece (10 mm × 10 mm × 10 mm) cut out from each silicon carbide ceramic honeycomb structure was placed in a measurement cell of an Autopore III manufactured by Micromeritics. After the pressure inside the cell was reduced, mercury was introduced to apply pressure, and the relationship between the pressure during pressurization and the volume of mercury forced into the pores present in the test piece was determined. The pressure was converted into pore diameter, and the cumulative pore volume (equivalent to the volume of mercury) integrated from the larger pore diameter side to the smaller pore diameter side was plotted against the pore diameter, to obtain a graph showing the relationship between pore diameter and cumulative pore volume. The pressure for introducing mercury was 0.5 psi (0.35 × 10 -3 kg / mm 2 The constants used to calculate the pore size from the pressure were a contact angle of 130° and a surface tension of 484 dyne / cm. The mercury pressure was 1800 psi (1.26 kg / mm 2 The cumulative pore volume of the pores (corresponding to a pore diameter of approximately 0.1 μm) was taken as the total pore volume. The porosity P (volume %) was calculated by multiplying the total pore volume V (cm 3 From the measured value of ρ (= 3.2 g / cm3), the true specific gravity of silicon carbide was calculated as ρ (= 3.2 g / cm3). 3 ) and calculated by the formula P = ρV / (1 + ρV) x 100. The median pore diameter was calculated by reading the pore diameter at which the cumulative pore volume was 50% of the total pore volume from a graph showing the relationship between pore diameter and cumulative pore volume. The results are shown in Table 3.

[0092] (g) Measurement of Coefficient of Thermal Expansion (CTE) Test specimens with a cross-sectional shape of 4.5 mm x 4.5 mm and a length of 50 mm were cut from each silicon carbide ceramic honeycomb structure, with the longitudinal direction approximately aligned with the flow path direction. Using a compression load / differential expansion thermomechanical analyzer (TMA, Thermo Plus, manufactured by Rigaku Corporation), each test specimen was heated from room temperature to 800°C at a heating rate of 10°C / min under a constant load of 20 g. The increase in length of the ceramic honeycomb structure in the overall length direction between room temperature and 800°C was measured. The measured values ​​were used as the average coefficient of thermal expansion between room temperature and 800°C. The results are shown in Table 3.

[0093] (h) Measurement of Thermal Shock Fracture Resistance Coefficient R The thermal shock fracture resistance coefficient R was calculated using the formula R = σ(1-ν) / αE (where σ is the maximum bending stress, E is Young's modulus, α is the thermal expansion coefficient, and ν is Poisson's ratio). The maximum bending stress σ and Young's modulus E were measured on test specimens cut from each silicon carbide ceramic honeycomb structure, each having a cross section of 10 mm x 10 mm and a length of 50 mm, using an Instron universal testing machine with a maximum load of 5 kN, in accordance with JIS R1602-1995, "Testing Methods for Elastic Modulus of Fine Ceramics." Specifically, the measurements were performed by a four-point bending test with an upper support distance of 20 mm, a lower support distance of 40 mm, and a loading rate of 0.5 mm / min. The Poisson's ratio ν was determined by determining the proportion (mass%) of each element in the SiC particles and the binder phase (oxide) from elemental mapping using EPMA, and then using the mixture rule described in the "(1) Silicon Carbide Particles" section. The measured Poisson's ratio ν for Examples 1 to 6 and Comparative Examples 1 to 3 was approximately 0.2. The thermal shock fracture resistance coefficient R was calculated using the above-mentioned formula using the maximum bending stress σ, Poisson's ratio ν, thermal expansion coefficient α, and Young's modulus E determined by the above-mentioned methods. Furthermore, the value of R for Comparative Example 2 was set to 1.00, and the values ​​are also expressed as the thermal shock fracture resistance coefficient R ratio, which is a relative value to that value. These results are shown in Table 3.

[0094]

[0095] Note: (1) Comparative Examples 1 to 3 do not include the second holding step.

[0096] Note: (1) t1 is the thickness of the SiO2 layer at the site where aggregates are bonded together without a binder phase. (2) t2 is the thickness of the SiO2 layer at the site where aggregates are bonded together with a binder phase. (3) No binder phase. (4) Not measured.

[0097] Note: (1) M1 = moles of cordierite phase / (moles of cordierite phase + moles of spinel phase). (2) No binder phase.

[0098] Notes: (1) CTE represents the average coefficient of thermal expansion from room temperature to 800°C. (2) σ represents the maximum bending stress. (3) E represents Young's modulus. (4) R represents the thermal shock fracture resistance coefficient. (5) The R ratio is the thermal shock fracture resistance coefficient ratio expressed as a relative value, with the thermal shock fracture resistance coefficient R of Comparative Example 2 set to 1.00.

[0099] Tables 2-1, 2-2, and 3 reveal that the silicon carbide-based ceramic honeycomb structures of Examples 1 to 6 of the present invention have a low thermal expansion coefficient, good thermal shock resistance, and maximum bending stress, and thus exhibit an excellent balance of low thermal expansion, thermal shock resistance, and strength. In contrast, the silicon carbide-based ceramic honeycomb structure of Comparative Example 1, which does not have a binder phase, has a low thermal expansion coefficient, but poor thermal shock resistance and a low maximum bending stress. The silicon carbide-based ceramic honeycomb structure of Comparative Example 2 has a significantly high thermal expansion coefficient because the mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase in the SiO2 layer is less than 3, and the mass ratio of the amorphous spinel phase to the crystalline spinel phase in the spinel phase is less than 3. Furthermore, the silicon carbide-based ceramic honeycomb structure of Comparative Example 3 has a high thermal expansion coefficient and a significantly low maximum bending stress because the molar ratio M1 of the cordierite phase is less than 0.2. Thus, it was found that Comparative Examples 1 to 3 were inferior to Examples 1 to 6 in terms of the balance of low thermal expansion, thermal shock resistance, and strength.

[0100] The silicon carbide ceramic honeycomb structure of the present invention does not require a non-oxidizing atmosphere during firing and the maximum firing temperature can be lowered, so it can be manufactured more cheaply than conventional structures and has low thermal expansion and thermal shock resistance, while also having an excellent balance between these properties and strength.

[0101] 1: aggregate 2: binder phase 3: SiO2 layer 4: spinel phase 5: cordierite phase 11, 21: outer wall 12, 22, 32: partition wall 13, 23, 33: outlet-side plugged flow passage (first flow passage) 14, 24, 34: inlet-side plugged flow passage (second flow passage) 15a, 25a, 35a: exhaust gas inlet-side end face 15b, 25b, 35b: exhaust gas outlet-side end face 16a, 26a, 36a: inlet-side plugging portion 16b, 26b, 36b: outlet-side plugging portion 100, 200: ceramic honeycomb filter 110: ceramic honeycomb structure 210: ceramic honeycomb segment bonded body 211, 311: honeycomb segment t1: thickness of SiO2 layer at a portion where aggregates are bonded without a binder phase t2: Thickness of the SiO2 layer at the point where aggregates are bonded together via the binder phase

Claims

1. A silicon carbide ceramic honeycomb structure having porous partition walls forming a plurality of flow paths penetrating from a first end face to a second end face, and an outer peripheral wall, wherein the partition walls have aggregates made of silicon carbide, an SiO2 layer present on the surface of the aggregates, and a binder phase containing a cordierite phase and a spinel phase, the aggregates have portions bonded to each other by the SiO2 layer without the binder phase and portions bonded to each other by the SiO2 layer via the binder phase, the SiO2 layer has an amorphous SiO2 phase and a crystalline SiO2 phase, and the silicon carbide ceramic honeycomb structure has a thermal expansion coefficient (between room temperature and 800°C) of 49 × 10 -7 / °C or less.

2. The silicon carbide ceramic honeycomb structure according to claim 1, characterized in that the spinel phase has an amorphous spinel phase and a crystalline spinel phase.

3. The silicon carbide ceramic honeycomb structure according to claim 2, characterized in that the mass ratio of the amorphous spinel phase to the crystalline spinel phase in the spinel phase is 3 or more.

4. A silicon carbide ceramic honeycomb structure according to claim 1, wherein the mass ratio of said amorphous SiO2 phase to said crystalline SiO2 phase in said SiO2 layer is 3 or more.

5. A silicon carbide ceramic honeycomb structure as described in claim 1, characterized in that the ratio (t1 / t2) of the thickness t1 of the SiO2 layer at the portion where the aggregates are bonded to each other by the SiO2 layer without the binder phase to the thickness t2 of the SiO2 layer at the portion where the aggregates are bonded to each other by the SiO2 layer via the binder phase is greater than 1.

6. A silicon carbide ceramic honeycomb structure as described in claim 1, characterized in that the molar ratio M1 of the cordierite phase in the binder phase [= number of moles of cordierite phase / (number of moles of cordierite phase+number of moles of spinel phase)] is 0.45 to 0.

90.

7. The silicon carbide ceramic honeycomb structure according to claim 1, characterized in that the total content of the cordierite phase and the spinel phase in the binder phase is 35 mass % or more.

8. A silicon carbide ceramic honeycomb structure having porous partition walls forming a plurality of flow paths penetrating from a first end face to a second end face, and an outer peripheral wall, wherein the partition walls have aggregates made of silicon carbide, an SiO2 layer present on the surface of the aggregates, and a binder phase containing a cordierite phase and a spinel phase, the spinel phase has an amorphous spinel phase and a crystalline spinel phase, and the mass ratio of the amorphous spinel phase to the crystalline spinel phase in the spinel phase is 3 or more, the aggregates have portions bonded to each other by the SiO2 layer without the binder phase and portions bonded to each other by the SiO2 layer via the binder phase, the SiO2 layer has an amorphous SiO2 phase and a crystalline SiO2 phase, and the mass ratio of the amorphous SiO2 phase to the crystalline SiO2 phase in the SiO2 layer is 3 or more, a molar ratio M1 of the cordierite phase in the binder phase [=number of moles of cordierite phase / (number of moles of cordierite phase+number of moles of spinel phase)] of 0.2 or more, and a thermal expansion coefficient (between room temperature and 800° C.) of the silicon carbide-based ceramic honeycomb structure is 49×10 -7 / °C or less.

9. A silicon carbide ceramic honeycomb structure as described in claim 1, characterized in that the flow path comprises first and second flow paths arranged alternately in the horizontal direction, the first flow path opens at the first end face and has a plugging portion at the second end face, and the second flow path has a plugging portion at the first end face and opens at the second end face.

10. The silicon carbide ceramic honeycomb structure according to claim 1, wherein in the cross section in the lateral direction, the cross-sectional area of ​​the first flow passage is larger than the cross-sectional area of ​​the second flow passage.

11. A ceramic honeycomb segment bonded body formed by bonding the outer wall surfaces of a plurality of honeycomb segments, characterized in that each of the honeycomb segments is made of a silicon carbide ceramic honeycomb structure described in any one of claims 1 to 9.

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