WO2022202903A1 - 炭化珪素質セラミックハニカム構造体及びその製造方法 - Google Patents

炭化珪素質セラミックハニカム構造体及びその製造方法 Download PDF

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WO2022202903A1
WO2022202903A1 PCT/JP2022/013530 JP2022013530W WO2022202903A1 WO 2022202903 A1 WO2022202903 A1 WO 2022202903A1 JP 2022013530 W JP2022013530 W JP 2022013530W WO 2022202903 A1 WO2022202903 A1 WO 2022202903A1
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Prior art keywords
particles
silicon carbide
ceramic honeycomb
honeycomb structure
phase
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PCT/JP2022/013530
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English (en)
French (fr)
Inventor
健一郎 清水
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日立金属株式会社
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Application filed by 日立金属株式会社 filed Critical 日立金属株式会社
Priority to US18/037,696 priority Critical patent/US11858857B2/en
Priority to KR1020237018005A priority patent/KR102590832B1/ko
Priority to CN202280008608.1A priority patent/CN116669830B/zh
Priority to EP22775685.5A priority patent/EP4230279A1/en
Priority to JP2022539769A priority patent/JP7205671B1/ja
Publication of WO2022202903A1 publication Critical patent/WO2022202903A1/ja

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    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/656—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes characterised by specific heating conditions during heat treatment
    • C04B2235/6567—Treatment time
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/658—Atmosphere during thermal treatment
    • C04B2235/6583—Oxygen containing atmosphere, e.g. with changing oxygen pressures
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/74—Physical characteristics
    • C04B2235/77—Density
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/70—Aspects relating to sintered or melt-casted ceramic products
    • C04B2235/80—Phases present in the sintered or melt-cast ceramic products other than the main phase
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/06—Ceramic, e.g. monoliths
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/30—Honeycomb supports characterised by their structural details
    • F01N2330/32—Honeycomb supports characterised by their structural details characterised by the shape, form or number of corrugations of plates, sheets or foils
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2330/00—Structure of catalyst support or particle filter
    • F01N2330/30—Honeycomb supports characterised by their structural details
    • F01N2330/48—Honeycomb supports characterised by their structural details characterised by the number of flow passages, e.g. cell density
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2370/00—Selection of materials for exhaust purification
    • F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors
    • F01N2370/04—Zeolitic material

Definitions

  • the present invention removes particulate matter (Particulate Matter (hereinafter sometimes referred to as "PM")) in the exhaust gas emitted from internal combustion engines such as diesel engines, etc., and purifies the exhaust gas.
  • PM particulate Matter
  • the present invention relates to a silicon carbide ceramic honeycomb structure used in a honeycomb filter and a manufacturing method thereof.
  • the NOx and PM contained in the exhaust gas of diesel engines can have a negative impact on the human body and the environment if they are released into the atmosphere.
  • a structure and a ceramic honeycomb filter for trapping PM are attached.
  • An example of a ceramic honeycomb filter for collecting PM in exhaust gas and purifying the exhaust gas is shown in FIGS. 1(a) and 1(b).
  • the ceramic honeycomb filter 100 includes a ceramic honeycomb structure 110 composed of porous partition walls 12 forming a plurality of channels 13 and 14 and an outer peripheral wall 11, an outflow-side plugged channel 13 and an inflow-side plugged channel 14.
  • the exhaust gas flows from the outflow-side sealed flow path 13 opening at the exhaust gas inflow-side end face 15a, and passes through the communication holes present on the surface and inside of the partition wall 12. and is discharged from the inflow-side sealed channel 14 opening at the outflow-side end surface 15b.
  • the exhaust gas passes through the communicating holes present on the surface and inside of the partition wall 12, PM in the exhaust gas is captured and the exhaust gas is purified.
  • the collected PM is burned and regenerated when the accumulated amount reaches a predetermined amount.
  • Such ceramic honeycomb structures are used in increasingly harsh environments, and it is known to use refractory particles such as silicon carbide (SiC) particles, which are excellent in thermal shock resistance, as their constituent materials.
  • Patent Document 1 uses silicon carbide powder having a specific surface area of 0.1 to 5 m 2 /g and an impurity component of 1.0 to 5.0% as a starting material, which is molded into a desired shape and dried. Later, it discloses a method of producing a catalyst carrier by sintering at a temperature in the range of 1600 to 2200°C. It states.
  • JP-A-6-182228 is a method of forming a sintered body using only silicon carbide powder as a starting material. Particles are bound together. Therefore, a very high firing temperature is required to form a fired body, and if a filter with a high porosity is to be manufactured, this sintering mechanism will not function sufficiently, resulting in a decrease in strength. There is In addition, since this method is a sintering method in which silicon carbide particles are bonded to each other by a recrystallization reaction of the silicon carbide powder itself, a very high firing temperature is required, resulting in high cost.
  • Patent Document 2 Japanese Patent Application Laid-Open No. 2002-201082 (Patent Document 2) can be manufactured at a relatively low firing temperature at a low cost, and has a high porosity that is sufficient to keep the pressure loss low when used as an automobile exhaust gas filter.
  • the following method is disclosed as a method for manufacturing a honeycomb structure having thermal conductivity. That is, Japanese Patent Application Laid-Open No. 2002-201082 discloses that a clay obtained by adding metal silicon and an organic binder to silicon carbide particles, mixing and kneading them, and molding them into a honeycomb shape, and calcining the obtained molded body. Disclosed is a method of manufacturing a honeycomb structure by removing the organic binder in the molded body and then firing it. The firing temperature is in the range of 1400 to 1600 ° C. It is described that a non-oxidizing atmosphere such as N 2 or Ar is preferable in a temperature range above the temperature at which the temperature starts.
  • a non-oxidizing atmosphere such as N 2 or
  • the honeycomb is sintered at a relatively low firing temperature of 1400 to 1600°C to ensure a sufficient porosity to keep the pressure loss low when used as a filter.
  • a structure can be obtained, it is desirable to perform firing in a non-oxidizing atmosphere in order to suppress oxidation, leading to high costs for firing equipment.
  • Patent Document 3 discloses a silicon carbide honeycomb structure having high porosity, high strength, and excellent thermal shock resistance, which is useful as a filter for which higher exhaust gas permeability is required. The following method is disclosed as a manufacturing method of. That is, Japanese Patent Application Laid-Open No. 2002-201082 discloses that a raw material mixture containing metal, silicon, carbon raw material and aluminum (Al) raw material is formed into a predetermined shape, degreased and fired to obtain 1 to 35% by mass of metal silicide and 0.5% by mass.
  • JP-A-2010-105861 sintering is performed at a relatively low temperature of 1250 to 1800° C. to obtain a silicon carbide-based porous body having excellent gas permeability and thermal shock resistance. Since it is necessary to perform firing in an atmosphere or a vacuum atmosphere, the cost of firing equipment is increased.
  • Patent Document 4 discloses an aggregate composed of a main aggregate composed of silicon carbide particles and a sub aggregate composed of at least one of mullite particles and alumina particles, and bonding the aggregates together. , a binder phase consisting of at least one of an amorphous phase and a cordierite phase, and a porous material having a porosity of 40 to 90%, forming a honeycomb structure with improved thermal shock resistance.
  • JP-A-2002-201082 is prepared by mixing silicon carbide powder as a main aggregate, powder as a sub-aggregate, and powder as a binding phase (binder powder), and if necessary Then, a binder, a surfactant, a pore-forming material, water, etc. are added to prepare a forming raw material, kneaded to form a clay, extruded to form a honeycomb formed body, dried and fired. can get.
  • JP-A-2002-201082 describes that the firing is preferably carried out at 1300-1600° C. in a non-oxidizing atmosphere such as nitrogen or argon.
  • an object of the present invention is to maintain the thermal shock resistance of a ceramic honeycomb structure used in a ceramic honeycomb filter, while using a firing process that does not require a firing temperature and a non-oxidizing atmosphere that are relatively lower than those of the prior art.
  • Another object of the present invention is to provide a silicon carbide ceramic honeycomb structure that can be manufactured at a lower cost than conventional ones, and a method for manufacturing the same.
  • the present inventors have attempted to maintain the thermal shock resistance of a ceramic honeycomb structure even when using a firing process that does not require a firing temperature that is relatively low and a non-oxidizing atmosphere.
  • the present invention was conceived as a result of intensive studies focusing on the raw material particles to be blended.
  • the partition walls preferably have a porosity of 35 to 50%.
  • the partition walls preferably have a median pore diameter of 5 to 20 ⁇ m.
  • the method of the present invention for producing a silicon carbide ceramic honeycomb structure is obtained by blending, mixing, and kneading silicon carbide particles, a binder containing at least alumina source particles and magnesia source particles, and an organic binder.
  • the kneaded clay is extruded into a honeycomb shape, and the obtained molded body is dried and then fired at a temperature of 1200 to 1350° C. in an air atmosphere.
  • the method for producing a silicon carbide ceramic honeycomb structure of the present invention it is preferable to blend 6 to 15% by mass of the alumina source particles and the magnesia source particles in total with respect to 100% by mass of the silicon carbide particles.
  • the alumina source particles of the binder are alumina particles or aluminum hydroxide particles
  • the magnesia source particles are magnesium oxide particles or magnesium hydroxide particles.
  • the present invention while maintaining thermal shock resistance as a ceramic honeycomb structure used for a ceramic honeycomb filter, a firing process that does not require a firing temperature and a non-oxidizing atmosphere that are relatively lower than those of the prior art is used. It is possible to provide a silicon carbide ceramic honeycomb structure that can be manufactured at a lower cost, and a method for manufacturing the same.
  • FIG. 1 is a front view schematically showing an example of a ceramic honeycomb filter
  • FIG. 2 is a partial cross-sectional view parallel to the axial direction schematically showing an example of a ceramic honeycomb filter
  • 1 is a perspective view schematically showing a ceramic honeycomb segment
  • FIG. 1 is a perspective view schematically showing an example of a ceramic honeycomb filter formed by joining and integrating;
  • the molar ratio M1 of the cordierite phase is obtained from [cordierite phase (mol)/(cordierite phase (mol) + spinel phase ( mol))]. If the molar ratio M1 of the cordierite phase is less than 0.4, the strength is lowered and the coefficient of thermal expansion is increased to deteriorate the thermal shock resistance.
  • the cordierite phase molar ratio M1 of the cordierite phase exceeds 0.9, the heat resistance is lowered and the porosity of the partition walls is lowered.
  • the cordierite phase molar ratio M1 is preferably between 0.45 and 0.70.
  • the bonding layer may contain other crystalline phases such as cristobalite, mullite, and forsterite, and amorphous phases in addition to cordierite and spinel phases.
  • the porosity of the partition walls when the porosity of the partition walls is 35 to 50%, the pressure loss of the silicon carbide ceramic honeycomb structure can be kept low and the strength can be maintained. If the porosity is less than 35%, the pressure loss of the ceramic honeycomb structure will increase, while if it exceeds 50%, it will be difficult to obtain sufficient strength.
  • the lower limit of porosity is preferably 38%, more preferably 40%.
  • the upper limit of porosity is preferably 49%, more preferably 48%.
  • the partition walls have a median pore diameter of 5 to 20 ⁇ m, so that the strength of the silicon carbide ceramic honeycomb structure can be maintained.
  • the lower limit of the median pore size is preferably 8 ⁇ m, more preferably 9 ⁇ m.
  • the upper limit of the median pore size is preferably 18 ⁇ m, more preferably 16 ⁇ m.
  • the silicon carbide ceramic honeycomb structure of the present invention is used as honeycomb segments 211, and as shown in FIG. A silicon ceramic honeycomb structure 210 may be used.
  • the plurality of honeycomb segments 211 are joined and integrated by the joining material layer 29, they are processed so that the outer peripheral shape of the cross section perpendicular to the flow path is circular, elliptical, triangular, square, or any other desired shape.
  • the outer peripheral surface is coated with a coating material to form the outer peripheral wall 21 .
  • the exhaust gas inflow side 25a or the exhaust gas outflow side 25b of the channel of the silicon carbide ceramic honeycomb structure 210 formed by joining and integrating is plugged alternately in a checkered pattern by a known method to form a ceramic honeycomb. It can be filter 200 .
  • the sealing portions 26a and 26b formed in the flow paths may be formed in the molded body before firing or the fired honeycomb segments before being joined, or may be formed in the bonding material layer 29. It may be formed after joining and integrating. These sealing portions may be formed on the exhaust gas inflow side or exhaust gas outflow side end face portion of the flow path, or may be formed at a position inside the flow path from the inflow side end face 25a or the outflow side end face 26b. good too.
  • silicon carbide particles as an aggregate, a binder containing at least alumina source particles and magnesia source particles, and an organic binder are blended and mixed.
  • the alumina source particles and magnesia source particles refer to particles of a compound containing alumina and particles of a compound containing magnesia, respectively, and further include particles of a compound containing alumina and magnesia.
  • the silicon carbide particles are contained as an aggregate, and the aggregates are bonded to each other via a bonding layer so as to form pores.
  • Silicon carbide particles preferably have an average particle size of 30 to 50 ⁇ m.
  • the bonding layer can contain at least a cordierite phase and a spinel phase.
  • the molar ratio M2 is determined by calculation as follows from the masses of the blended alumina source particles and magnesia source particles.
  • the lower limit of the molar ratio M2 is preferably 0.35, more preferably 0.40.
  • the upper limit is preferably 0.48.
  • alumina source particles and magnesia source particles in total with respect to 100% by mass of silicon carbide particles. If the content is less than 6% by mass, the bonding strength of the bonding layer that bonds the silicon carbide particles together will decrease, and the strength of the ceramic honeycomb structure will decrease. On the other hand, if it exceeds 15% by mass, the thermal shock resistance is lowered.
  • the lower limit of the sum of the alumina source particles and the magnesia source particles is preferably 7% by mass, more preferably 8% by mass with respect to 100% by mass of the silicon carbide particles.
  • the upper limit is preferably 14% by mass, more preferably 13% by mass.
  • the average particle size of the alumina source particles is preferably 1-15 ⁇ m. Moreover, the average particle size of the magnesia source particles is preferably 1 to 15 ⁇ m.
  • the alumina source particles are preferably alumina particles or aluminum hydroxide particles, and the magnesia source particles are preferably magnesium oxide particles or magnesium hydroxide particles.
  • alumina particles or aluminum hydroxide particles as the alumina source particles and magnesium oxide particles or magnesium hydroxide particles as the magnesia source particles, as will be described later, a lower firing temperature than before and a non-oxidizing atmosphere are required. It is preferable because it becomes possible to bake without It is particularly preferred to use alumina particles as the alumina source particles and magnesium hydroxide particles as the magnesia source particles as binders.
  • the binder in addition to these alumina source particles and magnesia source particles, spinel particles, mullite particles, forsterite particles, etc. made of compounds of alumina and/or magnesia may be included.
  • organic binders examples include methylcellulose, ethylcellulose, ethylmethylcellulose, carboxymethylcellulose, hydroxypropylmethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, and hydroxyethylethylcellulose. Among these, it is preferable to use hydroxypropylmethylcellulose and/or methylcellulose.
  • the organic binder is preferably contained in an amount of 5 to 15% by mass with respect to 100% by mass of the forming raw material (total of silicon carbide particles and binder).
  • water is added to the mixed raw materials and kneaded to form a plastic clay.
  • the content of water is adjusted so as to provide a moldable clay hardness, and is preferably 20 to 50% by mass based on the forming raw material.
  • the formed clay is extruded from a known honeycomb structure forming mold by a known extrusion method to form a honeycomb structure formed body. After drying the formed body, the end face, outer circumference, etc. are processed as necessary, and the body is fired in an oxidizing atmosphere at a temperature range of 1200 to 1350° C. to produce a silicon carbide ceramic honeycomb structure.
  • the drying method is not particularly limited, but examples include hot air drying, microwave heating drying, and high frequency heating drying.
  • the alumina source particles and magnesia source particles are sintered to form a bonding layer that bonds the silicon carbide particles together. Since sintering can be performed at a relatively low sintering temperature in this way, the sintering cost for forming the bonding layer can be kept lower than before. If the sintering temperature is less than 1200° C., the bonding between the silicon carbide particles and the binder phase is insufficient, and sufficient strength cannot be obtained. On the other hand, if the temperature exceeds 1350°C, the thermal shock resistance is lowered.
  • the firing temperature can be lowered, there is no need to perform firing in a non-oxidizing atmosphere for suppressing oxidation as in the conventional technology, and firing can be performed in an oxidizing atmosphere, so an increase in cost in the firing process can be suppressed.
  • Examples 1-10, Comparative Examples 2 and 3 Silicon carbide particles having particle diameters shown in Table 1 and binder particles (alumina source particles and magnesia source particles) were blended and mixed together with hydroxypropylmethyl cellulose as an organic binder in the amounts shown in Table 1 to be added. Water is added to the mixed raw materials and kneaded to form a plastic clay. A molded body with a honeycomb structure having a length of 304 mm was molded. After drying this compact in a hot air dryer at 120°C for 2 hours, it was fired in an oxidizing atmosphere at a maximum temperature of 1300°C to obtain a partition wall thickness of 8 mil (0.20 mm) and a cell density of 300 cpsi (46.5 cells/cm 2 ). ), silicon carbide ceramic honeycomb structures of Examples 1 to 10 and Comparative Examples 2 and 3 were obtained.
  • binder particles alumina source particles and magnesia source particles
  • Comparative example 1 The types and amounts of silicon carbide particles and binder particles were changed as shown in Table 1, and after the compact was dried with hot air, a degreasing process was added at 550°C for 3 hours, followed by argon at a maximum temperature of 1450°C. A silicon carbide ceramic honeycomb structure of Comparative Example 1 was obtained in the same manner as in Example 1, except that it was fired in the atmosphere for 2 hours.
  • Porosity and median pore diameter were measured by a mercury intrusion method.
  • a test piece (10 mm ⁇ 10 mm ⁇ 10 mm) cut from a ceramic honeycomb structure was placed in a measurement cell of Autopore III manufactured by Micromeritics. The relationship between the pressure during pressing and the volume of mercury forced into the pores existing in the test piece was obtained. The pressure is converted to a pore diameter, and the cumulative pore volume (corresponding to the volume of mercury) integrated from the larger pore diameter side to the smaller pore diameter side is plotted against the pore diameter, and the pore diameter and the cumulative pore volume are plotted.
  • the total pore volume and the median pore diameter which is the pore diameter at which the cumulative pore volume is 50% of the total pore volume, were determined.
  • A-axis compressive fracture strength is measured from a ceramic honeycomb structure with a diameter of 24.5 mm in accordance with the standard M505-87 "Testing method for ceramic monolith carriers for automotive exhaust gas purification catalysts" established by the Society of Automotive Engineers of Japan. And a sample piece with a length of 24.5 mm was taken.
  • Cordierite (molar ratio M1) cordierite (mol) / [cordierite (mol) + spinel (mol)]
  • Spinel (molar ratio) spinel (mol) / [cordierite (mol) + spinel (mol)]
  • the ceramic honeycomb filters of Examples 1 to 10 of the present invention had heat resistance equal to or higher than that of the ceramic honeycomb filters of Comparative Examples 1 to 3. It can be seen that it was possible to manufacture at low cost because it was possible to bake at a low maximum temperature without the need for

Abstract

炭化珪素質多孔質体の隔壁により仕切られた軸方向に貫通する多数の流路を有する炭化珪素質セラミックハニカム構造体であって、前記隔壁が、骨材となる炭化珪素粒子と、前記炭化珪素粒子を結合する結合層とを有し、前記結合層が、少なくともコーディエライト相とスピネル相とを含み、前記コーディエライト相のモル比M1［＝コーディエライト相/(コーディエライト相＋スピネル相)］が0.4～0.9であることを特徴とする炭化珪素質セラミックハニカム構造体。

Description

炭化珪素質セラミックハニカム構造体及びその製造方法
　本発明は、ディーゼルエンジン等の内燃機関から排出される排気ガス中の粒子状物質(Particulate Matter(以下、「PM」という場合がある。))等を除去し、排気ガスを浄化するためのセラミックハニカムフィルタに用いられる炭化珪素質セラミックハニカム構造体及びその製造方法に関する。
　ディーゼルエンジンの排気ガス中に含まれるNOxやPMが大気中に放出されると人体や環境に悪影響を与えるおそれがあるため、排気装置としてディーゼルエンジンの排気管の途中に、NOx触媒を担持したハニカム構造体、及びPMを捕集するためのセラミックハニカムフィルタを装着することが従来から行われている。排気ガス中のPMを捕集し排気ガスを浄化するためのセラミックハニカムフィルタの一例を図1(a)及び図1(b)に示す。セラミックハニカムフィルタ100は、複数の流路13、14を形成する多孔質の隔壁12と外周壁11とからなるセラミックハニカム構造体110と、流出側封止流路13及び流入側封止流路14の排気ガス流入側端面15a及び流出側端面15bを市松模様に交互に封止する流入側封止部16a及び流出側封止部16bとからなる。排気ガスは、図1(b)に点線矢印で示すように、排気ガス流入側端面15aに開口している流出側封止流路13から流入し、隔壁12の表面及び内部に存在する連通孔を通過し、流出側端面15bに開口している流入側封止流路14から排出される。排気ガスが隔壁12の表面及び内部に存在する連通孔を通過する際に、排気ガス中のPMが捕集され排気ガスの浄化が行われる。捕集されたPMは、その堆積量が所定の量になると燃焼して再生される。このようなセラミックハニカム構造体は、その使用環境が過酷になってきており、その構成材料として、耐熱衝撃性に優れる炭化珪素(SiC)粒子のような耐火性粒子を使用することが知られている。
　特開平6-182228号(特許文献1)は、比表面積が0.1～5m2/g及び不純物成分が1.0～5.0％の炭化珪素粉末を出発原料とし使用し、これを所望の形状に成形及び乾燥後、1600～2200℃の範囲で焼成して触媒担体を製造する方法を開示しており、優れた性能を有する多孔質炭化珪素質焼結体からなる触媒担体を経済的に製造することができると記載している。
　特開平6-182228号に記載の方法は、炭化珪素粉末のみを出発原料として焼結体を形成する方法であり、炭化珪素粒子表面から昇華した炭化珪素成分が粒子間に接触及び堆積することで粒子同士が結合される。従って、焼成体を形成するためには非常に高い焼成温度が必要であり、また高い気孔率を有するフィルターを製造しようとすると、この焼結機構が十分に機能しなくなるため、強度低下を招く場合がある。またこの方法は、炭化珪素粉末自体の再結晶反応により炭化珪素粒子同士を結合する焼結形態であるため、非常に高い焼成温度が必要となりコスト高を招く。
　特開2002-201082号(特許文献2)は、比較的低い焼成温度で安価に製造できるとともに、自動車排気ガスフィルタとして用いた場合の圧力損失を低く抑えるのに十分な気孔率が確保され、高い熱伝導率を有したハニカム構造体の製造方法として以下の方法を開示している。すなわち、特開2002-201082号は、炭化珪素粒子に金属珪素と有機バインダーとを添加し混合及び混練して得られた坏土をハニカム形状に成形し、得られた成形体を仮焼して成形体中の有機バインダーを除去した後、本焼成することによりハニカム構造体を製造する方法を開示しており、本焼成の温度が1400～1600℃の範囲であり、本焼成の雰囲気は、酸化が始まる温度以上の温度域においてはN2、Ar等の非酸化雰囲気とするのが好ましいと記載している。
　特開2002-201082号に記載の方法では、1400～1600℃の比較的低い焼成温度で焼結させて、フィルターとして用いた場合の圧力損失を低く抑えるのに十分な気孔率が確保されたハニカム構造体を得ることができるものの、酸化を抑制するために非酸化雰囲気で焼成することが望ましく、焼成設備へのコスト高を招く。
　特開2010-105861号(特許文献3)は、より高い排気ガス透過性能が要求されるフィルターとして有用な、高気孔率でありながら高強度で、耐熱衝撃性に優れた炭化珪素質ハニカム構造体の製造方法として以下の方法を開示している。すなわち、特開2002-201082号は、金属、珪素、炭素原料及びアルミニウム(Al)原料を含む原料混合物を所定形状に成形し、脱脂及び焼成して、1～35質量％の金属珪化物及び0.5～10質量％のアルミナ(Al2O3)を含有し、38～80％の気孔率を有する炭化珪素質多孔体を製造する方法を開示しており、焼成温度が1250～1800℃であり、焼成雰囲気は不活性雰囲気が好ましいと記載している。
　特開2010-105861号に記載の方法では、1250～1800℃の比較的低温で焼結して、ガス透過性能と耐熱衝撃性に優れた炭化珪素質多孔体を得られるものの、アルゴン(Ar)雰囲気や真空雰囲気で焼成を行う必要があるため、焼成設備へのコスト高を招く。
　国際公開2013/146954号(特許文献4)は、炭化珪素粒子からなる主骨材と、ムライト粒子及びアルミナ粒子の少なくとも一方からなる副骨材とからなる骨材と、前記骨材同士を結合する、非晶質相及びコージェライト相の少なくとも一方からなる結合相とからなり、40～90％の気孔率を有する多孔質材料を開示しており、耐熱衝撃性を向上させたハニカム構造体を形成することが可能だと記載している。特開2002-201082号に記載の多孔質材料は、主骨材となる炭化珪素粉末と、副骨材となる粉末と、結合相となる粉末(結合材粉末)とを混合し、必要に応じて、バインダ、界面活性剤、造孔材、水等を添加して、成形原料を作製し、混練して坏土を形成し、押出成形してハニカム成形体を形成し、乾燥、焼成して得られる。特開2002-201082号は、焼成は、窒素、アルゴン等の非酸化雰囲気下で1300～1600℃で行うのが好ましいと記載している。
　国際公開2013/146954号に記載の方法では、1300～1600℃の温度で焼結して耐熱衝撃性に優れた多孔質材料が得られるものの、焼成は、窒素、アルゴン等の非酸化雰囲気下で行う必要があるため、焼成設備へのコスト高を招く。
　以上説明したように、セラミックハニカムフィルタに用いられるセラミックハニカム構造体の構成材料として、炭化珪素(SiC)粒子のような耐火性粒子を使用する場合、非常に高い焼成温度や非酸化雰囲気で行う必要があり、これらの条件を満たすことが可能な焼成炉を用いるとコスト高を招いていた。従って、さらに安価に製造できる方法の開発が望まれている。
　従って、本発明の目的は、セラミックハニカムフィルタに用いられるセラミックハニカム構造体としての耐熱衝撃性を維持しつつ、従来よりも比較的低い焼成温度と、非酸化雰囲気を必要としない焼成工程を用いて、従来より安価に製造できる炭化珪素質セラミックハニカム構造体、及びその製造方法を提供することにある。
　上記目的に鑑み、本発明者は、従来よりも比較的低い焼成温度と、非酸化雰囲気を必要としない焼成工程を用いても、セラミックハニカム構造体としての耐熱衝撃性を維持できるようにするために、配合する原料粒子に着目して、鋭意検討した結果本発明に想到した。
　すなわち、本発明の炭化珪素質セラミックハニカム構造体は、炭化珪素質多孔質体の隔壁により仕切られた軸方向に貫通する多数の流路を有する炭化珪素質セラミックハニカム構造体であって、前記隔壁が、骨材となる炭化珪素粒子と、前記炭化珪素粒子を結合する結合層とを有し、前記結合層が、少なくともコーディエライト相とスピネル相とを含み、前記コーディエライト相のモル比M1［＝コーディエライト相/(コーディエライト相＋スピネル相)］が0.4～0.9であることを特徴とする。
　本発明の炭化珪素質セラミックハニカム構造体において、前記隔壁の気孔率は35～50％であるのが好ましい。
　本発明の炭化珪素質セラミックハニカム構造体において、前記隔壁のメジアン細孔径は5～20μmであるのが好ましい。
　炭化珪素質セラミックハニカム構造体を製造する本発明の方法は、炭化珪素粒子と、少なくともアルミナ源粒子及びマグネシア源粒子を含む結合材と、有機バインダーとを配合し、混合、及び混練して得られた坏土をハニカム形状に押出成形し、得られた成形体を乾燥後、1200～1350℃の温度範囲で、大気雰囲気下で焼成することを特徴とする。
　本発明の炭化珪素質セラミックハニカム構造体の製造方法において、前記アルミナ源粒子及び前記マグネシア源粒子を、モル比M2［＝(Al2O3)/(Al2O3+ MgO)］0.32～0.50で配合するのが好ましい。
　本発明の炭化珪素質セラミックハニカム構造体の製造方法において、前記炭化珪素粒子100質量％に対して、前記アルミナ源粒子及び前記マグネシア源粒子を合計で6～15質量％配合するのが好ましい。
　本発明の炭化珪素質セラミックハニカム構造体の製造方法において、前記結合材のアルミナ源源粒がアルミナ粒子又は水酸化アルミニウム粒子であり、マグネシア源粒子が酸化マグネシウム粒子又は水酸化マグネシウム粒子であるのが好ましい。
　本発明によれば、セラミックハニカムフィルタに用いられるセラミックハニカム構造体としての耐熱衝撃性を維持しつつ、従来よりも比較的低い焼成温度と、非酸化雰囲気を必要としない焼成工程を用いて、従来より安価に製造できる炭化珪素質セラミックハニカム構造体、及びその製造方法を提供することができる。
セラミックハニカムフィルタの一例を模式的に示す正面図である。 セラミックハニカムフィルタの一例を模式的に示す軸方向に平行な部分断面図である。 セラミックハニカムセグメントを模式的に示す斜視図である。 接合一体化して形成されたセラミックハニカムフィルタの一例を模式的に示す斜視図である。
　以下、図面を参照しつつ本発明の実施の形態について説明する。本発明は、以下の実施形態に限定されるものではなく、発明の範囲を逸脱しない限りにおいて、変更、修正、改良を加え得るものである。
[1]セラミックハニカム構造体
　本発明の炭化珪素質セラミックハニカム構造体は、炭化珪素質多孔質体の隔壁により仕切られた軸方向に貫通する多数の流路を有し、前記隔壁が、骨材となる炭化珪素粒子と、前記炭化珪素粒子を結合する結合層とを有し、前記結合層が、少なくともコーディエライト相とスピネル相とを含み、前記コーディエライト相のモル比M1［＝コーディエライト相/(コーディエライト相＋スピネル相)］が0.4～0.9である。
　結合層が、少なくともコーディエライト相とスピネル相とを含み、前記コーディエライト相のモル比M1［＝コーディエライト相/(コーディエライト相＋スピネル相)］が0.4～0.9にあることで、結合層の強度が十分に得られるとともに、十分な耐熱衝撃性を得ることができる。ここで、コーディエライト相のモル比M1とは、コーディエライト相のモル数とスピネル相のモル数から、［コーディエライト相(モル)/(コーディエライト相(モル)＋スピネル相(モル))］で算出される比率のことである。コーディエライト相のモル比M1が0.4未満の場合、強度が低下するとともに、熱膨張係数が大きくなり耐熱衝撃性が悪化する。一方、コーディエライト相のモル比M1が0.9を超える場合、耐熱性が低下し、隔壁の気孔率が低下する。コーディエライト相のモル比M1は好ましくは0.45～0.70である。結合層は、コーディエライト相とスピネル相との他に、クリストバライト、ムライト、フォルステライト等その他の結晶相、及び非結晶相を含んでも良い。
　コーディエライト相のモル比M1［＝コーディエライト相/(コーディエライト相＋スピネル相)］は次のようにして求めることができる。まず焼成されたセラミックハニカム構造体の一部を粉末状にしてＸ線回折測定を行い、得られた粉末回折チャートからコーディエライトの（110）面のピーク強度、及びスピネルの（311）面のピーク強度よりセラミックハニカム構造体全体におけるコーディエライトとスピネルとの質量比を算出する。得られた質量比から、コーディエライト1モルの質量を585.0及びスピネル1モルの質量を142.3として、コーディエライトとスピネルとのモル比に換算し、コーディエライト相とスピネル相との合計に対するコーディエライト相のモル比M1を求める。
　本発明の炭化珪素質セラミックハニカム構造体において、隔壁の気孔率が35～50％であることで、炭化珪素質セラミックハニカム構造体の圧力損失を低く維持できるとともに、強度を維持することができる。気孔率が35％未満の場合、セラミックハニカム構造体の圧力損失が大きくなり、一方、50％を超えると、十分な強度が有られ難くなる。気孔率の下限は好ましくは38％、より好ましくは40％である。一方、気孔率の上限は好ましくは49％、より好ましくは48％である。
　本発明の炭化珪素質セラミックハニカム構造体において、隔壁のメジアン細孔径が5～20μmであることで、炭化珪素質セラミックハニカム構造体の強度を維持することができる。メジアン細孔径が5μm未満の場合、セラミックハニカム構造体の圧力損失が大きくなり、一方、20μmを超えると、十分な強度が有られ難くなる。メジアン細孔径の下限は好ましくは8μm、より好ましくは9μmである。一方、メジアン細孔径の上限は好ましくは18μm、より好ましくは16μmである。
　図2に示すように、本発明の炭化珪素質セラミックハニカム構造体をハニカムセグメント211とし、図3に示すように、複数のハニカムセグメント211を接合材層29によって接合一体化して、接合された炭化珪素質セラミックハニカム構造体210としても良い。複数のハニカムセグメント211を接合材層29によって接合一体化した後は、その流路に直交する断面の外周形状が円形、楕円形、三角形、四角形、その他所望の形状となるように加工し、加工後の外周面にコーティング材を被覆して、外周壁21を形成する。
　接合一体化して形成された炭化珪素質セラミックハニカム構造体210の流路の排気ガス流入側25a又は排気ガス流出側25bを公知の方法で交互に市松模様となるように目封止してセラミックハニカムフィルタ200とすることができる。ここで、流路に形成される封止部26a、26bは、焼成する前の成形体、又は接合される前の焼成済のハニカムセグメントに対して形成しても良いし、接合材層29で接合一体化した後に形成しても良い。これらの封止部は流路の排気ガス流入側又は排気ガス流出側の端面部に形成しても良いし、流入側端面25a又は流出側端面26bから流路内部に入った位置に形成してもよい。
[2]炭化珪素質セラミックハニカム構造体の製造方法
　本発明の炭化珪素質セラミックハニカム構造体の製造方法について、その一実施形態を説明する。
　まず、骨材となる炭化珪素粒子と、少なくともアルミナ源粒子及びマグネシア源粒子を含む結合材と、有機バインダーとを配合し混合する。ここでアルミナ源粒子及びマグネシア源粒子は、それぞれアルミナを含む化合物の粒子及びマグネシアを含む化合物の粒子のことであり、さらにアルミナ及びマグネシアを含む化合物の粒子を含む。炭化珪素粒子は、骨材として含有し、骨材同士が結合層を介して細孔を形成するように結合されているものである。炭化珪素粒子は、平均粒子径が30～50μmであるのが好ましい。
　結合材としてのアルミナ源粒子及びマグネシア源粒子は、モル比M2［＝(Al2O3)/(Al2O3 + MgO)］を0.32～0.50で配合するのが好ましい。このような配合比にすることで、結合層が少なくともコーディエライト相とスピネル相とを含むようにできる。モル比M2は、配合したアルミナ源粒子とマグネシア源粒子の質量から以下のようにして計算によって決定する。すなわち、アルミナ源粒子及びマグネシア源粒子中のアルミナ分(Al2O3)のモル数とマグネシア分(MgO)のモル数とを算出し、アルミナ分(Al2O3)及びマグネシア分(MgO)の合計モル数に対するアルミナ分(Al2O3)のモル数を、モル比M2［＝(Al2O3)/(Al2O3 + MgO)］として表す。
　例えば、アルミナ源として酸化アルミニウム［Al(OH)3］、マグネシア源として酸化マグネシウム［Mg(OH)2］を使用した場合、酸化アルミニウム中のアルミナ分、及び酸化マグネシウム中のマグネシア分は、それぞれ
　Al(OH)3＝(1/2)Al2O3＋(3/2)H2O、及び
　Mg(OH)2＝MgO＋H2O
と表されるので、酸化アルミニウム1モルあたりのアルミナ分は0.5モル、酸化マグネシウム1モル中のマグネシア分は1モルと計算できる。この関係から、前述したようにアルミナ分及びマグネシア分のモル数を求め、モル比M2を求める。またアルミナ及びマグネシアの両方を含む化合物（例えば、スピネル）の粒子を用いた場合も同様に、この化合物中のアルミナ分(Al2O3)及びマグネシア分(MgO)を算出してモル比M2を求める。
　モル比M2が0.32未満の場合、及びモル比M2が0.50を超える場合、耐熱衝撃性が低下する。モル比M2の下限は好ましくは0.35、さらに好ましくは0.40である。上限は好ましくは0.48である。
　この時、炭化珪素粒子100質量％に対して、アルミナ源粒子とマグネシア源粒子の合計を6～15質量％配合するのが好ましい。6質量％未満の場合、炭化珪素粒子同士を結合する結合層の結合強度が低下し、セラミックハニカム構造体の強度が低下する。一方、15質量％を超える場合、耐熱衝撃性が低下する。炭化珪素粒子100質量％に対して、アルミナ源粒子とマグネシア源粒子の合計の下限は、好ましくは7質量％、より好ましくは8質量％である。一方、上限は、好ましくは14質量％、より好ましくは、13質量％である。
　アルミナ源粒子の平均粒子径は、1～15μmであるのが好ましい。また、マグネシア源粒子の平均粒子径は、1～15μmであるのが好ましい。
　アルミナ源粒子はアルミナ粒子又は水酸化アルミニウム粒子であるのが好ましく、マグネシア源粒子は酸化マグネシウム粒子又は水酸化マグネシウム粒子であるのが好ましい。アルミナ源粒子としてアルミナ粒子又は水酸化アルミニウム粒子、及びマグネシア源粒子として酸化マグネシウム粒子又は水酸化マグネシウム粒子を用いることで、後述するように、従来よりも低い焼成温度で、かつ非酸化雰囲気を必要とせずに焼成することが可能となるので好ましい。アルミナ源粒子としてアルミナ粒子、及びマグネシア源粒子として水酸化マグネシウム粒子を結合材として用いるのが特に好ましい。結合材として、これらのアルミナ源粒子及びマグネシア源粒子以外に、アルミナ及び/又はマグネシアの化合物からなるスピネル粒子、ムライト粒子、フォルステライト粒子等を含んでも良い。
　有機バインダーは、メチルセルロース、エチルセルロース、エチルメチルセルロース、カルボキシメチルセルロース、ヒドロキシプロピルメチルセルロース、ヒドロキシエチルセルロース、ヒドロキシメチルセルロース、ヒドロキシエチルエチルセルロース等を挙げることができる。これらの中でも、ヒドロキシプロピルメチルセルロース、及び/又はメチルセルロースを用いるのが好ましい。有機バインダーは、成形原料(炭化珪素粒子と結合材の合計)100質量％に対して5～15質量％含有するのが好ましい。
　次に、混合した原料に水を添加して混練して可塑性の坏土を形成する。水の含有量は、成形可能な坏土の硬度となるように調整されるが、成形原料に対して20～50質量％であるのが好ましい。
　形成された坏土を公知のハニカム構造体成形用の金型から、公知の押出成形法により押出成形して、ハニカム構造の成形体を形成する。この成形体を乾燥後、必要により端面、外周等の加工を施し、1200～1350℃の温度範囲で、酸化雰囲気で焼成することにより炭化珪素質セラミックハニカム構造体を製造する。
　乾燥の方法は、特に限定されないが、例えば、熱風乾燥、マイクロ波加熱乾燥、高周波加熱乾燥等の方法を挙げることができる。
　1200～1350℃の温度範囲で焼成を行うことで、アルミナ源粒子とマグネシア源粒子が焼結により炭化珪素粒子同士を結合する結合層となる。このように比較的低い焼成温度で焼成が可能なので、結合層を形成するための焼成コストを従来よりも低く抑えることができる。焼成温度が1200℃未満の場合、炭化珪素粒子と結合相との結合が不十分となり、十分な強度を得られない。一方、1350℃を超える場合、耐熱衝撃性が低下する。また、焼成温度を低くできるため、従来技術のように、酸化を抑制するために非酸化雰囲気で行う必要が無く、酸化雰囲気で焼成を行うことができるので、焼成工程におけるコスト増を抑制できる。
　以下、本発明を実施例に基づいてさらに詳細に説明するが、本発明は、これらの実施例に限定されるものではない。
実施例1～10、比較例2及び3
　表1に示す粒径を有する炭化珪素粒子、及び結合材の粒子(アルミナ源粒子及びマグネシア源粒子)を表1に示す添加量で有機バインダーとしてヒドロキシプロピルメチルセルロースとともに配合し混合した。混合した原料に水を添加して混練して可塑性の坏土を形成し、得られた坏土をハニカム構造体成形用の金型からスクリュー成形機により押出して、一辺が34 mmの外形四角形柱状で長さ304 mmのハニカム構造の成形体を成形した。この成形体を熱風乾燥機にて120℃で2時間乾燥後、1300℃の最高温度で酸化雰囲気で焼成して、隔壁厚さ8 mil(0.20 mm)及びセル密度300 cpsi(46.5セル/cm2)を有する実施例1～10、比較例2及び3の炭化珪素質セラミックハニカム構造体を得た。
比較例1
　炭化珪素粒子及び結合材の粒子の種類及び添加量を表1に示すように変更し、さらに成形体を熱風乾燥した後に550℃で3時間の脱脂工程を追加し、1450℃の最高温度でアルゴン雰囲気で2時間焼成した以外は実施例1と同様にして、比較例1の炭化珪素質セラミックハニカム構造体を得た。
　得られた実施例1～10及び比較例1～3の炭化珪素質セラミックハニカム構造体の1個を用いて、気孔率、メジアン細孔径、熱膨張係数、及びA軸圧縮強度の測定を以下の通り行った。結果を表2に示す。
(a)気孔率、及びメジアン細孔径の測定
　気孔率、及びメジアン細孔径は、水銀圧入法により測定を行った。セラミックハニカム構造体から切り出した試験片(10 mm×10 mm×10 mm)を、Micromeritics社製オートポアIIIの測定セル内に収納し、セル内を減圧した後、水銀を導入して加圧し、加圧時の圧力と試験片内に存在する細孔中に押し込まれた水銀の体積との関係を求めた。前記圧力を細孔径に換算し、細孔径の大きい側から小さい側に向かって積算した累積細孔容積(水銀の体積に相当)を細孔径に対してプロットし、細孔径と累積細孔容積との関係を示すグラフを得た。水銀を導入する圧力は0.5psi(0.35×10-3 kg/mm2)とし、圧力から細孔径を算出する際の常数は、接触角=130°及び表面張力=484 dyne/cmの値を使用した。なお水銀の加圧力が1800psi(1.26kg/mm2、細孔径約0.1μmに相当)での累積細孔容積を全細孔容積とした。
　得られた水銀圧入法の測定結果から、全細孔容積、及び累積細孔容積が全細孔容積の50%となる細孔径であるメジアン細孔径を求めた。
(b)熱膨張係数の測定
　熱膨張係数は、4.5 mm×4.5 mmの断面形状及び50 mmの長さの試験片を、長手方向が流路方向にほぼ一致するように切り出し、熱機械分析装置(TMA、リガク社製ThermoPlus、圧縮荷重方式/示差膨張方式)を用いて、一定荷重20 gをかけながら、昇温速度10℃/minで室温から800℃まで加熱した時の全長方向の長さの増加量を測定して、40～800℃間の平均熱膨張係数として求めた。
(c)A軸圧縮破壊強度
　A軸圧縮破壊強度は、社団法人自動車技術会が定める規格M505-87「自動車排気ガス浄化触媒用セラミックモノリス担体の試験方法」に従い、セラミックハニカム構造体から直径24.5 mm及び長さ24.5 mmの試料片を採取して行った。
Figure JPOXMLDOC01-appb-T000001
 注(1)：モル比M2［=(Al2O3)/(Al2O3 + MgO)］
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
 注(1)：コーディエライト(モル比M1)=コーディエライト(モル)/［コーディエライト(モル)＋スピネル(モル)］
注(2)：スピネル(モル比)=スピネル(モル)/［コーディエライト(モル)＋スピネル(モル)］
 
　表1及び2から、実施例1～10の本発明のセラミックハニカムフィルタは、比較例1～3のセラミックハニカムフィルタに対して、耐熱性が同等以上であるにもかかわらず、焼成時に非酸化雰囲気を必要とせず、最高温度を低く焼成できたため、安価に製造できたことがわかる。

Claims (7)

  1. 　炭化珪素質多孔質体の隔壁により仕切られた軸方向に貫通する多数の流路を有する炭化珪素質セラミックハニカム構造体であって、前記隔壁が、骨材となる炭化珪素粒子と、前記炭化珪素粒子を結合する結合層とを有し、前記結合層が、少なくともコーディエライト相とスピネル相とを含み、前記コーディエライト相のモル比M1［＝コーディエライト相/(コーディエライト相＋スピネル相)］が0.4～0.9であることを特徴とする炭化珪素質セラミックハニカム構造体。
  2. 　前記隔壁の気孔率が35～50％であることを特徴とする請求項1に記載の炭化珪素質セラミックハニカム構造体。
  3. 　前記隔壁のメジアン細孔径が5～20μmであることを特徴とする請求項1又は2に記載の炭化珪素質セラミックハニカム構造体。
  4. 　炭化珪素粒子と、アルミナ源粒子及びマグネシア源粒子を含む結合材と、有機バインダーとを配合し、混合、及び混練して得られた坏土をハニカム形状に押出成形し、得られた成形体を乾燥後、1200～1350℃の温度範囲で、大気雰囲気下で焼成することを特徴とする請求項1～3に記載の炭化珪素質セラミックハニカム構造体を製造する方法。
  5. 　前記アルミナ源粒子及び前記マグネシア源粒子を、モル比M2［＝(Al2O3)/(Al2O3+ MgO)］0.32～0.50で配合することを特徴とする請求項4に記載の炭化珪素質セラミックハニカム構造体の製造方法。
  6. 　前記炭化珪素粒子100質量％に対して、前記アルミナ源粒子及び前記マグネシア源粒子を合計で6～15質量％配合することを特徴とする請求項4又は5に記載の炭化珪素質セラミックハニカム構造体の製造方法。
  7. 　前記結合材のアルミナ源粒子がアルミナ粒子又は水酸化アルミニウム粒子であり、マグネシア源粒子が酸化マグネシウム粒子又は水酸化マグネシウム粒子であることを特徴とする請求項4～6のいずれかに記載の炭化珪素質セラミックハニカム構造体の製造方法。
     
     
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