JP2010105860A - Silicon carbide-based porous body and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a silicon carbide-based porous body which has high strength, a high heat conductivity and excellent thermal shock resistance although it has high porosity and can be produced by sintering at a relatively low temperature. <P>SOLUTION: The silicon carbide-based porous body contains metal silicide of 1-35 mass% and boron (B) of 0.1-10 mass% expressed in terms of boron oxide (B<SB>2</SB>O<SB>3</SB>), and has porosity of 38-80%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a silicon carbide based porous body and a honeycomb structure suitable as, for example, a filter for purifying diesel exhaust gas, and a method for producing a silicon carbide based porous body.

  Honeycomb structure is widely used as a collection filter for exhaust gas, for example, diesel particulate filter (DPF) for capturing and removing particulate matter (particulate) contained in exhaust gas from diesel engines, etc. Has been.

  Such a honeycomb structure is disposed so that a plurality of cells that are partitioned and formed by porous partition walls made of, for example, silicon carbide (SiC) are parallel to each other in the central axis direction. Have a structure. Moreover, the edge part of the adjacent cell is plugged alternately (in a checkered pattern). That is, one cell is open at one end and the other end is sealed, and another cell adjacent thereto is sealed at one end and the other end is open. is doing. By adopting such a structure, the exhaust gas flowing into a predetermined cell (inflow cell) from one end is passed through a cell (outflow cell) adjacent to the inflow cell by passing through a porous partition wall. When the particulate matter (particulates) in the exhaust gas is captured by the partition wall when it is allowed to flow out and pass through the partition wall, the exhaust gas can be purified.

  As a specific related technique for a structure using silicon carbide as a constituent material, silicon carbide powder having a predetermined specific surface area and impurity content is used as a starting material, which is molded into a desired shape, dried, and 1600 to A honeycomb structure porous silicon carbide catalyst carrier obtained by firing in a temperature range of 2200 ° C. is disclosed (see, for example, Patent Document 1).

JP-A-6-182228 Japanese Patent Publication No. 8-10621 Japanese Patent No. 3699992

  According to the sintering form (necking) by recrystallization reaction of silicon carbide powder itself disclosed in Patent Document 1, the silicon carbide component evaporates from the surface of the silicon carbide particles, and this is the contact portion (neck portion) between the particles. As a result of condensation, the neck portion grows and a combined state is formed. However, in order to evaporate silicon carbide, a very high firing temperature is required. This increases the cost, and a material having a high coefficient of thermal expansion must be fired at a high temperature, so that the firing yield is lowered. There was a problem.

  On the other hand, a ceramic heater formed by a porous silicon carbide sintered body containing a nickel silicide alloy in the grain boundary is disclosed (for example, see Patent Document 2). However, according to the manufacturing method described in Patent Document 2, the porosity of the obtained silicon carbide sintered body is about 35%. For this reason, it can be said that this silicon carbide sintered body is insufficient for filter applications that require higher gas permeation performance. Moreover, since it is necessary to perform baking at a high temperature of about 2000 ° C., there are problems in terms of cost and manufacturing yield.

  Further, silicon carbide having a porosity of 95 to 97% obtained by firing a sponge-like porous structure such as a resin impregnated with a slurry containing silicon and a carbon source in order to provide a structural material having a higher porosity. A porous structure material is disclosed (for example, see Patent Document 3). However, the porous structural material disclosed in Patent Document 3 exhibits excellent gas permeation performance because of its high porosity, but there is a problem that the strength is insufficient because the porosity is too high. is there.

  Further, a silicon carbide based porous body obtained by simply mixing silicon and carbon or silicon and carbon and silicon carbide and performing reaction sintering at about 1450 ° C. in an atmosphere of argon or the like does not contain silicon. Therefore, closed pores are easily formed at the positions, and open pores useful as a filter are difficult to be formed. Therefore, the filter characteristics (gas permeability) were low.

  The present invention has been made in view of such problems of the prior art, and the object is to provide high strength while having high porosity, high thermal conductivity and high thermal shock resistance. An object of the present invention is to provide a silicon carbide porous body and a honeycomb structure that are excellent and can be manufactured by sintering at a relatively low temperature, and a simple method for manufacturing a silicon carbide structure.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that the above-mentioned problems can be achieved by containing metal silicide and boron at a predetermined ratio, and the present invention is completed. It came to.

  That is, according to the present invention, the following silicon carbide porous body, honeycomb structure, and method for producing a silicon carbide porous body are provided.

[1] Silicon carbide containing 1 to 35% by mass of metal silicide, 0.1 to 10% by mass of boron (B) in terms of boron oxide (B ₂ O ₃ ), and a porosity of 38 to 80% Porous material.

[2] The silicon carbide based porous material according to [1], wherein the strength is 10 to 50 MPa.

[3] The silicon carbide based porous material according to [1] or [2], wherein all silicon carbide contained as a main component is β-SiC.

[4] The above [1], which contains α-SiC and β-SiC, and the content ratio of the β-SiC with respect to the total of the α-SiC and the β-SiC is 5% by mass or more and less than 100% by mass The silicon carbide based porous material according to [2].

[5] The silicon carbide based porous material according to [3] or [4], wherein at least a part of the β-SiC has a particle size of 20 μm or more.

[6] The silicon carbide based porous material according to any one of [1] to [5], wherein the metal silicide is nickel silicide.

[7] The silicon carbide based porous material according to any one of [1] to [6], wherein the thermal conductivity is 5 to 50 W / mK.

[8] A honeycomb-shaped honeycomb structure having a plurality of cells partitioned by partition walls, comprising the silicon carbide based porous material according to any one of [1] to [7].

[9] While combining and integrating a plurality of honeycomb-shaped segments having a plurality of cells partitioned by partition walls, which are made of the silicon carbide based porous material according to any one of [1] to [7]. A honeycomb structure obtained by plugging a predetermined opening of the cell with one end face of the segment and plugging the remaining opening of the cell with the other end face of the segment.

[10] The honeycomb structure according to [8] or [9], which is used as a filter for purifying diesel exhaust gas.

[11] A raw material mixture containing metal, silicon, carbon, and boron (B) raw materials is formed into a predetermined shape, degreased, and fired to obtain 1 to 35% by mass of metal silicide and boron (B) to boron oxide ( B ₂ O _3), respectively 0.1 to 10% contained in terms of the method for manufacturing the silicon carbide based porous material porosity to obtain a silicon carbide-based porous body is 38 to 80%.

[12] The method for producing a silicon carbide based porous material according to [11], wherein the raw material mixture further includes an α-SiC raw material.

[13] The method for producing a silicon carbide based porous material according to [11] or [12], wherein firing is performed at 1250 to 1800 ° C. in an argon (Ar) atmosphere or a vacuum atmosphere.

[14] The method for producing a silicon carbide based porous material according to any one of [11] to [13], wherein the boron (B) raw material is metal B.

[15] The method for producing a silicon carbide based porous material according to any one of [11] to [14], wherein the raw material mixture is formed into a honeycomb shape having a plurality of cells partitioned by partition walls.

  The silicon carbide based porous material of the present invention has an effect that it has a high strength even though it has a high porosity, a high thermal conductivity, excellent thermal shock resistance, and can be produced by sintering at a relatively low temperature. Is.

  The honeycomb structure of the present invention has high porosity and high strength, high thermal conductivity, excellent thermal shock resistance, and can be manufactured by sintering at a relatively low temperature. is there. For this reason, the honeycomb structure of the present invention is suitable as a diesel exhaust gas purifying filter (DPF) or the like.

  According to the method for producing a silicon carbide based porous material of the present invention, a silicon carbide based porous material having high porosity but high strength, high thermal conductivity and excellent thermal shock resistance is sintered at a relatively low temperature. It can manufacture simply by making it tie.

  BEST MODE FOR CARRYING OUT THE INVENTION The best mode for carrying out the present invention will be described below, but the present invention is not limited to the following embodiment, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. It should be understood that modifications and improvements as appropriate to the following embodiments also fall within the scope of the present invention.

1. Silicon carbide based porous material:
One embodiment of the silicon carbide based porous material of the present invention contains 1 to 35% by mass of metal silicide and 0.1 to 10% by mass of boron (B) in terms of boron oxide (B ₂ O ₃ ), The porosity is 38 to 80%. The details will be described below.

(Metal silicide)
Metal silicide (hereinafter also referred to as “metal silicide”) is a reaction product of metal and silicon (Si). The silicon carbide based porous material of the present invention contains this metal silicide in a predetermined ratio, and therefore has high thermal conductivity and excellent thermal shock resistance. In addition, when the silicon carbide based porous body of the present invention is manufactured according to the manufacturing method described later, the silicon acts on the reaction in the process of forming silicon carbide by the reaction of silicon and carbon, and the silicon carbide particles generated by the reaction It is presumed to affect the diameter and shape. For this reason, it is considered that a silicon carbide based porous material having a highly porous structure can be formed.

  The ratio of the metal silicide contained in the silicon carbide based porous material of the present invention is 1% by weight or more, preferably 2% by weight or more, when the entire silicon carbide based porous material is 100% by weight. Preferably it is 3 mass% or more, and an upper limit is 35 mass% or less, Preferably it is 33 mass% or less, More preferably, it is 30 mass% or less. When the content ratio of the metal silicide is less than 1% by mass, the thermal conductivity is not sufficiently high, and the effect of improving the thermal shock resistance is insufficient. In addition, the pore connectivity is reduced. On the other hand, if the content ratio of the metal silicide is more than 30% by mass, the thermal expansion coefficient tends to be high, and the thermal shock resistance may be lowered.

  Specific examples of suitable metal silicides include nickel silicide, zirconium silicide, iron silicide, titanium silicide, tungsten silicide, and the like. Among these, nickel silicide and zirconium silicide are more preferable because thermal conductivity can be further increased, and a highly porous structure can be obtained, and nickel silicide is particularly preferable.

Metal silicide is a compound represented by various chemical formulas. For example, some nickel silicides are represented by chemical formulas such as Ni ₃ Si, Ni ₅ Si ₂ , Ni ₂ Si, NiSi, and NiSi ₂ . Among these, NiSi ₂ is preferable from the viewpoint of heat resistance. Zirconium silicide includes those represented by chemical formulas such as Zr ₃ Si, Zr ₂ Si, Zr ₅ Si ₃ , Zr ₃ Si ₂ , Zr ₅ Si ₄ , Zr ₆ Si ₅ , ZrSi, and ZrSi ₂ . Of these, ZrSi ₂ is preferable from the viewpoint of heat resistance.

(Boron)
When the silicon carbide based porous material of the present invention is manufactured according to the manufacturing method described later, B added as a B (boron) raw material is converted into a SiC reaction between silicon (silicon (Si)) and carbon (C) in the raw material mixture. Further, the SiC sintering reaction is promoted, and thereby the grain growth of the generated SiC is promoted to form a thick SiC skeleton, and the filter characteristics, particularly the strength and the thermal conductivity are improved. Specifically, the grain growth is twice or more as compared with the case where B is not added.

The ratio of B contained in the silicon carbide based porous material of the present invention is such that the lower limit is 0.1% by mass or more in terms of B ₂ O ₃ when the entire silicon carbide based porous material is 100% by mass. Preferably it is 0.2 mass% or more, More preferably, it is 0.3 mass% or more, and an upper limit is 10 mass% or less, Preferably it is 9 mass% or less, More preferably, it is 8 mass% or less. If the B content in terms of B ₂ O ₃ is less than 0.1% by mass, the amount of B in the production method cannot be said to be sufficient, and the effect of promoting the grain growth of SiC is insufficient. On the other hand, when the content ratio of B in terms of B ₂ O ₃ is more than 10% by mass, grain growth may be suppressed.

(Silicon carbide)
The silicon carbide based porous material of the present invention has silicon carbide as its main component. Silicon carbide has polymorphs such as α-SiC and β-SiC, but the silicon carbide based porous material of the present invention has all the silicon carbide contained in β-SiC or α-SiC and β-SiC. It is preferable that both are contained. In the case of containing both α-SiC and β-SiC, the lower limit of the content ratio of β-SiC to the total of α-SiC and β-SiC is preferably 5% by mass or more, and more preferably Is 10% by mass or more, particularly preferably 15% by mass or more, and the upper limit is preferably less than 100% by mass, more preferably 80% by mass or less, and particularly preferably 50% by mass or less. When the content ratio of β-SiC is within the above numerical range, the strength can be made sufficient. In addition, it exists in the tendency for intensity | strength to become inadequate that the content rate of (beta) -SiC is less than 5 mass%.

  The silicon carbide constituting the silicon carbide based porous material of the present invention usually contains at least a part of β-SiC in the form of particles. The particle size of the particulate β-SiC (hereinafter also simply referred to as “particle size”) is preferably 20 μm or more, more preferably 25 μm or more, and particularly preferably 30 μm or more. When the particle diameter of β-SiC is 20 μm or more, the strength can be made sufficient. The upper limit of the particle size of β-SiC is not particularly limited, but is 100 μm or less from the viewpoint of substantial manufacturability and the like. Here, the “β-SiC particle size” referred to in the present specification is an arbitrary magnification (for example, 500 times or 1000 times) when an arbitrary cross section of the silicon carbide based porous material is observed with an electron microscope. The maximum β-SiC particle size (maximum length: the maximum length at two points on the contour of the particle image) is measured and repeated this several times (for example, 20 times). The value obtained by dividing the total β-SiC particle size by the number of fields of view.

(Porosity)
The silicon carbide based porous material manufactured according to the manufacturing method described later is a process in which silicon carbide is formed by the reaction of silicon and carbon, the metal acts on the reaction, and the particle size and shape of silicon carbide produced by the reaction It is speculated that it will affect. For this reason, the resulting pores are likely to be open pores. The porosity is easily affected by the composition of the composition (particularly the proportion of silicon). The porosity of the silicon carbide based porous material of the present invention can be controlled in a wide range. Specifically, the lower limit is 38% or more, preferably 40% or more, more preferably 45% or more, and the upper limit is 80% or less, preferably 75% or less, more preferably 70% or less. When the porosity is less than 38%, the gas permeation coefficient decreases, and the pressure loss that occurs when the gas permeates increases. On the other hand, if the porosity exceeds 80%, the strength decreases. The “porosity” referred to in this specification refers to a value measured by the Archimedes method (based on JIS R 1634).

(Thermal conductivity)
The silicon carbide based porous material of the present invention contains a metal silicide at a predetermined ratio, and therefore has high thermal conductivity and excellent thermal shock resistance. Specifically, the lower limit of the thermal conductivity of the silicon carbide based porous material of the present invention is preferably 5 W / mK or more, more preferably 7 W / mK or more, particularly preferably 10 W / mK or more, and the upper limit is It is preferable that it is 50 W / mK or less. If the thermal conductivity is less than 5 W / mK, the thermal shock resistance tends to decrease. On the other hand, if the thermal conductivity is more than 50 W / mK, there is no particular problem, but it is substantially difficult to manufacture.

(Strength)
Since the silicon carbide based porous material of the present invention promotes the grain growth of SiC particles at the time of production by boron contained at a predetermined ratio, it exhibits excellent strength while having high porosity. Specifically, the lower limit of the strength of the silicon carbide based porous material of the present invention is preferably 10 MPa or more, more preferably 12 MPa or more, particularly preferably 15 MPa or more, and the upper limit is preferably 50 MPa or less, more preferably. 45 MPa or less, particularly preferably 40 MPa or less. If the strength is less than 10 MPa, there is a possibility that breakage occurs when used for DPF or the like. On the other hand, if the strength exceeds MPa, there is no particular problem, but it is practically difficult to produce a product having such strength while ensuring the porosity required for a filter such as DPF. In addition, "strength" as used in this specification means the value measured by the bending strength test based on JISR1601.

2. Method for producing silicon carbide based porous material:
Next, the manufacturing method of the silicon carbide based porous material of the present invention will be described. In one embodiment of the method for producing a silicon carbide based porous material of the present invention, a raw material mixture containing metal, silicon, carbon and boron (B) raw materials is formed into a predetermined shape, degreased, and fired to obtain a metal silicide. 1 to 35% by mass, boron (B) is contained in an amount of 0.1 to 10% by mass in terms of boron oxide (B ₂ O ₃ ), and a silicon carbide based porous material having a porosity of 38 to 80% is obtained. is there. The details will be described below.

(metal)
A metal is a component that can react with silicon (silicon (Si)) to form a metal silicide. In addition, by including a metal in the raw material mixture, in the process of forming silicon carbide by the reaction of silicon and carbon, the metal acts on the reaction and affects the particle size and shape of the silicon carbide produced by the reaction. Presumed to give. For this reason, the resulting pores are likely to be open pores. In addition, the porosity is affected by the preparation composition (particularly the proportion of silicon). For this reason, according to the manufacturing method of the silicon carbide based porous material of the present invention, the porosity can be controlled in a wide range.

  The type of metal is not particularly limited as long as it can react with silicon (silicon (Si)) to generate metal silicide. Specific examples of suitable metals include nickel (Ni), zirconium (Zr), iron (Fe), titanium (Ti), tungsten (W) and the like. Of these, nickel (Ni) and zirconium (Zr) are preferable, and nickel (Ni) is more preferable. In addition, these metals can be used individually by 1 type or in combination of 2 or more types. Moreover, the metal compound containing these metals can also be used besides a metal simple substance.

  As the metal, a powder (particulate) is usually used. When using powdered metal (metal powder), from the viewpoint of reactivity with silicon (Si), the lower limit of the particle size of the metal powder is preferably 1 μm or more, more preferably 2 μm or more, and the upper limit is Preferably it is 100 micrometers or less, More preferably, it is 80 micrometers or less.

(silicon)
Silicon (silicon (Si)) is a component capable of generating metal silicide by reacting with the above-described metal, and a component capable of generating silicon carbide by reacting with carbon (C) described later. Silicon (Si) is usually used in the form of powder (particulate). When powdered silicon (silicon powder) is used, the lower limit of the particle size of the silicon powder is preferably 1 μm or more, more preferably 2 μm or more, and the upper limit is preferably 100 μm from the viewpoint of reactivity with metal. Hereinafter, it is more preferably 80 μm or less.

(carbon)
Carbon (C) is a component that can react with the aforementioned silicon (Si) to produce silicon carbide. Carbon (C) is usually used in the form of powder (particulate). When using powdered carbon (carbon powder), from the viewpoint of reactivity with silicon (Si), the particle size of the carbon powder has a lower limit of preferably 5 nm or more, more preferably 10 nm or more, and an upper limit of Preferably it is 50 micrometers or less, More preferably, it is 30 micrometers or less. As such fine carbon powder, carbon black can be suitably used. Further, from the viewpoint of reactivity with silicon (Si), it is preferable to use amorphous carbon rather than crystalline such as graphite.

(Boron raw material)
Boron (B) has the effect of promoting the SiC-forming reaction and sintering reaction between silicon (silicon (Si)) and carbon (C) in the raw material mixture, and thereby the SiC produced by the SiC-forming reaction. Grain growth is promoted to form a thick SiC skeleton, and filter characteristics, particularly strength and thermal conductivity, are improved. As a boron (B) raw material, boron compounds such as boron carbide (B ₄ C) and boron oxide (B ₂ O ₃ ) can be used in addition to metal boron.

(Α-SiC raw material)
The raw material mixture preferably further contains an α-SiC raw material. As the α-SiC raw material, particulate α-SiC can be suitably used. The lower limit of the average particle diameter of the particulate α-SiC is preferably 5 μm or more, more preferably 10 μm or more, and the upper limit is preferably 100 μm or less, more preferably 80 μm or less. When the average particle diameter of the particulate α-SiC is less than 5 μm, thermal characteristics such as thermal conductivity tend to be lowered. On the other hand, when the average particle diameter of the particulate α-SiC is more than 100 μm, there is no particular problem, but it may be difficult to mold. The “average particle size” referred to in the present specification is a value obtained by measuring the particle size distribution by a laser diffraction scattering method in accordance with JIS R 1629, and is a volume-based average particle size.

(Raw material mixture)
In addition to the metal, silicon, carbon, boron raw material, and α-SiC raw material described above, for example, an organic or inorganic binder, a pore-forming agent, a surfactant (or dispersant), and water are included in the raw material mixture. Etc. Specific examples of the organic or inorganic binder include methyl cellulose, hydroxypropoxyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose, and polyvinyl alcohol.

  Specific examples of the pore-forming agent include graphite, wheat flour, starch, phenol resin, polymethyl methacrylate, polyethylene, polyethylene terephthalate, foamed resin (acrylonitrile plastic balloon), water-absorbing resin, and the like. Specific examples of surfactants (or dispersants) include fatty acid salts, alkyl sulfate esters, polyoxyethylene alkyl ether sulfate esters, alkyl benzene sulfonates, alkyl naphthalene sulfonates, alkyl sulfosuccinates, alkyls. Diphenyl ether disulfonate, alkyl phosphate, polycarboxylate, aliphatic quaternary ammonium salt, aliphatic amine salt, polyoxyethylene alkyl ether, polyoxyethylene alcohol ether, polyoxyethylene glycerin fatty acid ester, polyoxyethylene Sorbitan (or sorbitol) fatty acid ester, polyethylene glycol fatty acid ester, alkylbetaine, amine oxide, cationic cellulose derivative, polyethyleneimine, polycarboxylic Salts, may be mentioned polyacrylic acid salts.

  The raw material mixture is mixed and kneaded to form a plastic clay, and this clay is molded into a predetermined shape to obtain a molded body. The shape of the molded body is not particularly limited, and can be various shapes depending on applications. However, when it is used as a diesel exhaust gas purification filter or the like, it is preferably a honeycomb shape having a plurality of cells partitioned by partition walls. In order to form the clay into such a honeycomb shape, it is preferable to employ a forming method such as extrusion.

  If the obtained molded body is dried by an appropriate drying method and then baked, a silicon carbide based porous body which is an embodiment of the present invention can be produced. The drying method is not particularly limited, but for example, a drying method using microwaves, hot air or the like is preferable. In addition, since the silicon carbide contained in the obtained silicon carbide based porous body usually contains β-SiC that is a low-temperature phase, the firing temperature can be made relatively low. Specifically, the firing temperature is preferably 1250 to 1800 ° C, more preferably 1300 to 1750 ° C, and particularly preferably 1350 to 1700 ° C. If the firing temperature is less than 1250 ° C., sintering may not proceed sufficiently. On the other hand, if the firing temperature is higher than 1800 ° C., a special firing furnace may be required, and it tends to be disadvantageous in terms of cost and production yield. Firing is preferably performed in an inert atmosphere, more preferably performed in an argon (Ar) atmosphere or a vacuum atmosphere. Particularly when firing is performed in a vacuum atmosphere, the aggregate SiC (α-SiC) and metal silicidation are used. Bonding with SiC (β-SiC) generated by a product or reaction is strengthened.

  After drying the molded body and before firing, appropriately calcination (also referred to as degreasing, debinding, etc.) to burn and remove organic substances (binder, dispersant, pore former, etc.) in the molded body It can be carried out. In general, the combustion temperature of the organic binder is about 100 to 300 ° C., and the combustion temperature of the pore former is about 200 to 800 ° C. Therefore, the calcining temperature may be about 200 to 1000 ° C. Although there is no restriction | limiting in particular as a calcination time, Usually, it is about 1 to 10 hours. The atmosphere can be selected as appropriate, such as an air atmosphere or a nitrogen atmosphere.

3. Honeycomb structure:
Next, the honeycomb structure of the present invention will be described. FIG. 1 is a perspective view showing an embodiment of the honeycomb structure of the present invention. As shown in FIG. 1, the honeycomb structure 11 of the present embodiment has a plurality of cells 15 partitioned by porous partition walls 16. The cell 15 is a portion serving as a flow path for various fluids such as gas and liquid. In FIG. 1, reference numeral 10 indicates an outer wall of the honeycomb structure 1. The honeycomb structure 11 of the present embodiment is constituted by the above-mentioned silicon carbide porous body. For this reason, the honeycomb structure 11 of the present embodiment has high strength while having high porosity, high thermal conductivity, and excellent thermal shock resistance. It can also be manufactured by sintering at a relatively low temperature.

  FIG. 2 is a perspective view showing another embodiment of the honeycomb structure of the present invention. FIG. 3 is an enlarged view of a main part of the honeycomb structure shown in FIG. A honeycomb structure 1 shown in FIGS. 2 and 3 is obtained by integrally bonding honeycomb segments 2 with a bonding material layer 9 formed of a bonding material composition. The honeycomb segment 2 has a structure in which a plurality of cells 5 defined by porous partition walls 6 are arranged so as to be parallel to each other in the central axis direction. And the whole structure of the honeycomb structure 1 is configured by being assembled in a direction perpendicular to the central axis of the honeycomb structure 1.

  The honeycomb segments 2 integrally bonded by the bonding material layer 9 are bonded so that the overall shape of the cross section perpendicular to the flow path (cell 5) is circular, elliptical, triangular, square, or other desired shape. The outer peripheral surface is covered with the coating material 4. When this honeycomb structure 1 is used as a DPF, each cell 5 of the honeycomb segment 2 is alternately plugged with a filler 7 at one end as shown in FIG.

  In the predetermined cell 5 (inflow cell), the left end side in FIG. 4 and FIG. 5 is open, while the right end side is plugged with the filler 7, and another cell 5 (outflow) adjacent to this is filled. In the cell), the left end side is plugged with the filler 7, but the right end side is open. By such plugging, as shown in FIG. 3, the end surface of the honeycomb segment 2 has a checkered pattern.

  FIG. 5 shows a case where the left side of the honeycomb segment 2 serves as an exhaust gas inlet, and the exhaust gas flows into the honeycomb segment 2 from the open cells 5 (inflow cells) without being plugged. The exhaust gas flowing into the cell 5 (inflow cell) passes through the porous partition wall 6 and flows out from the other cell 5 (outflow cell). When passing through the partition walls 6, particulate matter (particulates) containing soot in the exhaust gas is captured by the partition walls 6. In this way, exhaust gas can be purified. Due to such trapping, particulates containing soot accumulate with time in the honeycomb segment 2 and the pressure loss increases, so that regeneration processing for burning soot and the like is periodically performed. 3 to 5 show the honeycomb segment 2 having a square cross section perpendicular to the flow path (cell 5), the shape may be a triangle, a hexagon, or the like.

  Further, the cross-sectional shape of the cell 5 may be a triangle, a hexagon, a circle, an ellipse, or other shapes in addition to the square as shown in FIG. The cell 5 need not have a single cross-sectional shape. For example, a combination of an octagon and a quadrangle is a preferred embodiment. In particular, the inflow cell is preferably an octagon and the outflow cell is preferably a quadrangle. With such a combination, while the particulate deposition capacity of the inflow cell can be increased, a large amount of deposited particulates burns during regeneration, and a large amount of heat is generated. Therefore, the thermal conductivity obtained by the present invention is high. This is because a silicon carbide based porous material excellent in thermal shock resistance becomes more effective.

  As shown in FIG. 3, the bonding material layer 9 is a layer formed by applying a bonding material composition to the outer peripheral surface of the honeycomb segment 2 and functions to bond adjacent honeycomb segments 2 together. . In addition, as a joining material composition, the thing of the composition similar to the clay used in order to manufacture the silicon carbide based porous body which is embodiment of this invention can be used suitably.

  The bonding material composition may be applied to the outer peripheral surface of each honeycomb segment 2, but may be applied to only one of the corresponding outer peripheral surfaces between adjacent honeycomb segments 2. Such application to only one side of the corresponding surface is preferable in that the amount of the bonding material composition used can be saved. The direction in which the bonding material composition is applied is not particularly limited, such as the longitudinal direction in the outer peripheral surface of the honeycomb segment, the direction perpendicular to the longitudinal direction in the outer peripheral surface of the honeycomb segment, and the direction perpendicular to the outer peripheral surface of the honeycomb segment. The coating is preferably performed in the longitudinal direction in the outer peripheral surface of the honeycomb segment. The thickness of the bonding material layer 9 is determined in consideration of the bonding force between the honeycomb segments 2 and is appropriately selected within a range of 0.5 to 3.0 mm, for example.

  As the filler 7 used for plugging the cells 5, the same material as the clay can be used. The plugging with the filler 7 is performed by, for example, filling the open cells 5 by immersing the end faces of the honeycomb segments 2 in a slurry-like filler in a state where the cells 5 that are not plugged are masked. Can be done. Filling of the filler 7 may be performed before or after firing after the formation of the honeycomb segment 2, but is preferably performed before firing because the firing process is completed once.

  After the honeycomb segment 2 as described above is manufactured, a paste-like bonding material composition is applied to the outer peripheral surface of the honeycomb segment 2 to form a bonding material layer 9, and a predetermined three-dimensional shape (the entire structure of the honeycomb structure 1) is formed. ), A plurality of honeycomb segments 2 are assembled so as to be pressure-bonded in this assembled state, and then dried by heating. In this manner, a joined body in which the plurality of honeycomb segments 2 are integrally joined is manufactured. Thereafter, the joined body is ground into the above-described shape, and the outer peripheral surface is covered with the coating material 4 and heated and dried. In this way, the honeycomb structure 1 shown in FIG. 1 is manufactured. As the material of the coating material 4, the same material as that of the bonding material layer 9 can be used. The thickness of the coating material 4 is appropriately selected within a range of 0.1 to 1.5 mm, for example.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In addition, the measuring method of various physical-property values and the evaluation method of various characteristics are shown below.

  [Average particle diameter of various raw material powders]: Measured according to JIS R 1629.

  [Particle diameter of β-SiC particles]: A sample cut into a cubic shape (5 × 5 × 5 mm) was impregnated with a resin, and then the polished surface was polished and observed with an electron microscope at a magnification of 500 times (20 Field of view), and the maximum particle diameter (maximum particle diameter) of β-SiC particles in each field of view was measured. A value obtained by dividing the total of the maximum particle diameters by the number of fields of view (20) was defined as “particle diameter of β-SiC particles”.

[Identification and quantification of crystal phase]: The crystal phase was identified and quantified by powder X-ray diffraction. Quantitative analysis uses powder X-ray diffraction for SiC, and “New SiC-based ceramic materials—Recent developments”, Japan Society for the Promotion of Science, High Temperature Ceramic Materials 124th Committee, Uchida Otsukaku (2001) p. . It was based on the quantitative analysis method described in 347-350. For NiSi ₂ or ZrSi ₂ , the metal silicide phase was confirmed to be NiSi ₂ or ZrSi ₂ by powder X-ray diffraction, and from the Ni content or Zr content obtained by chemical analysis, NiSi ₂ or ZrSi ₂ The value converted into was calculated.

  [Porosity]: Measured by Archimedes method (based on JIS R 1634) on a sample cut into a 5 × 5 × 25 mm or 0.3 × 30 × 30 mm size shape.

  [Strength]: Measured according to JIS R 1601.

  [Thermal conductivity]: Measured according to JIS R 1611 using a sample cut into a size of φ10 × 2 mm or 0.3 × 10 × 10 mm.

(Example 1 (Batch No. 1))
Based on 100 parts by mass of a mixture containing 1.5% by mass of nickel (Ni) powder (# 350), 72.5% by mass of silicon (Si) powder (particle size: 78 μm), and 26.0% by mass of carbon black 1.0 parts by mass of boron (B) powder, 1 part by mass of a surfactant and 9 parts by mass of an organic binder were added, and an appropriate amount of water was added to obtain a raw material mixture. The obtained raw material mixture was molded into a size of 25 × 50 × 10 mm by uniaxial pressure molding, and then dried under temperature conditions of room temperature and 120 ° C. to obtain a dried molded body. The obtained dried molded body was calcined at 350 ° C. for 5 hours in an air atmosphere, and then fired at 1450 ° C. in an Ar inert atmosphere to obtain a plate-like silicon carbide based porous body (Example 1). It was. As shown in Table 2, the crystal phase of the metal silicide contained in the obtained silicon carbide based porous material was represented by the chemical formula “NiSi ₂ ”, and the content ratio was 3 mass%. Moreover, the particle diameter of β-SiC was 10 μm, and the content ratio of β-SiC was 100% by mass when the total of α-SiC and β-SiC was 100% by mass. Furthermore, the content ratio of B in terms of B ₂ O ₃ was 1.8% by mass. Furthermore, the porosity was 58%, the strength was 20 MPa, and the thermal conductivity was 9 W / mK.

(Examples 2 to 12, Comparative Examples 1 to 4, 6, and 7 (Batch Nos. 2 to 12, 20 to 23, 25, and 26))
Batch Nos. Shown in Table 1 for the composition of the raw material mixture are shown. Except for blending 2-12, 20-23, 25, 26, a plate-like silicon carbide based porous material (Examples 2-12, Comparative Examples 1-4) in the same manner as in Example 1 above. 6, 7) were obtained. The type and content ratio of the crystalline phase of the metal silicide contained in each of the obtained silicon carbide based porous bodies, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and B in terms of B ₂ O ₃ Table 2 shows the content ratio. In addition, Table 2 shows the porosity, strength, and thermal conductivity of each obtained silicon carbide based porous material.

(Examples 13 to 19, Comparative Example 8 (Batch No. 13 to 19, 27))
Batch Nos. Shown in Table 1 for the composition of the raw material mixture are shown. A plate-like silicon carbide porous body (implemented in the same manner as in Example 1 above) except that the blending of 13 to 19 and 27 is performed and the calcined molded body is fired in a vacuum atmosphere. Examples 13 to 19 and Comparative Example 8) were obtained. The type and content ratio of the crystalline phase of the metal silicide contained in each of the obtained silicon carbide based porous bodies, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and B in terms of B ₂ O ₃ Table 2 shows the content ratio. In addition, Table 2 shows the porosity, strength, and thermal conductivity of each obtained silicon carbide based porous material.

(Examples 20 to 22, Comparative Example 5 (Batch No. 2, 5, 7, 24))
Batch Nos. Shown in Table 1 for the composition of the raw material mixture are shown. A plate-like silicon carbide porous body (as in the case of Example 1 described above) except that the composition of 2, 5, 7, 24 and the calcined molded body are fired at 1800 ° C. Examples 20 to 22 and Comparative Example 5) were obtained. The type and content ratio of the crystalline phase of the metal silicide contained in each of the obtained silicon carbide based porous bodies, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and B in terms of B ₂ O ₃ Table 2 shows the content ratio. In addition, Table 2 shows the porosity, strength, and thermal conductivity of each obtained silicon carbide based porous material.

(Example 23)
Batch No. shown in Table 1 The raw material mixture of 5 was mixed and kneaded to prepare a plastic clay. The produced clay was extruded and dried, and the partition wall thickness was 310 μm, the cell density was about 46.5 cells / cm ² (300 cells / square inch), and the cross-sectional shape perpendicular to the flow path (cell) However, a honeycomb formed body having a regular square having a side length of 35 mm and a total length of 152 mm was obtained. After calcining at 350 ° C. for 5 hours in an air atmosphere, firing was performed at about 1450 ° C. in an Ar inert atmosphere to obtain a porous honeycomb structure (Example 23). As shown in Table 3, the crystal phase of the metal silicide contained in the obtained honeycomb structure was represented by the chemical formula “NiSi ₂ ”, and the content ratio was 24 mass%. Moreover, the particle size of β-SiC was 20 μm, and the content ratio of β-SiC was 100% by mass when the total of α-SiC and β-SiC was 100% by mass. Furthermore, the content ratio of B in terms of B ₂ O ₃ was 1.7% by mass. Furthermore, the porosity was 60%, the strength was 18 MPa, and the thermal conductivity was 12 W / mK.

(Example 24)
Batch No. shown in Table 1 In place of the raw material mixture of 5 A porous honeycomb structure (Example 24) was obtained in the same manner as in Example 23 described above except that the raw material mixture of 13 was used and the honeycomb formed body was fired in a vacuum atmosphere. It was. The type and content ratio of the crystalline phase of the metal silicide contained in the obtained honeycomb structure, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and the content ratio of B in terms of B ₂ O ₃ are shown. 3 shows. In addition, Table 3 shows the porosity, strength, and thermal conductivity of the obtained honeycomb structure.

(Example 25)
A porous honeycomb structure (Example 25) was obtained in the same manner as in Example 23 except that the honeycomb formed body was fired at 1800 ° C. The type and content ratio of the crystalline phase of the metal silicide contained in the obtained honeycomb structure, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and the content ratio of B in terms of B ₂ O ₃ are shown. 3 shows. In addition, Table 3 shows the porosity, strength, and thermal conductivity of the obtained honeycomb structure.

(Example 26)
Batch No. shown in Table 1 The raw material mixture of 5 was mixed and kneaded to prepare a plastic clay. The produced clay was extruded and dried, and the partition wall thickness was 310 μm, the cell density was about 46.5 cells / cm ² (300 cells / square inch), and the cross-sectional shape perpendicular to the flow path (cell) However, a honeycomb formed body having a regular square having a side length of 35 mm and a total length of 152 mm was obtained. Both ends of the cells of the obtained honeycomb formed body were plugged with the same material as the above-mentioned clay so that adjacent cells were sealed with the opposite ends. After drying, it was calcined at 350 ° C. for 5 hours in an air atmosphere, and then fired at about 1450 ° C. in an Ar inert atmosphere to obtain a porous honeycomb structure (honeycomb segment). A process of applying a bonding material (ceramic cement) to the outer wall surface of the obtained honeycomb segment to form a bonding material layer having a thickness of about 1 mm and placing another honeycomb segment on the formed bonding material layer is repeated. A laminate composed of 16 (4 × 4) honeycomb segments was produced. After pressurizing appropriately and joining the whole, it dried at 140 degreeC for 2 hours, and obtained the joined body. After the outer periphery of the obtained joined body is cut into a cylindrical shape, a coating material (ceramic cement (according to the joining material)) is applied to the outer peripheral surface (cut surface), and dried at 700 ° C. for 2 hours to be cured. To obtain a honeycomb structure (DPF) (Example 26).

As shown in Table 4, the crystal phase of the metal silicide contained in the obtained DPF was represented by the chemical formula “NiSi ₂ ”, and the content ratio was 24 mass%. Moreover, the particle size of β-SiC was 20 μm, and the content ratio of β-SiC was 100% by mass when the total of α-SiC and β-SiC was 100% by mass. Furthermore, the content ratio of B in terms of B ₂ O ₃ was 1.7% by mass. Furthermore, the porosity was 60%, the strength was 18 MPa, and the thermal conductivity was 12 W / mK.

(Example 27)
Batch No. shown in Table 1 In place of the raw material mixture of 5 A DPF (Example 27) was obtained in the same manner as in Example 26 described above except that the raw material mixture of 13 was used and the honeycomb formed body was fired in a vacuum atmosphere. Table 4 shows the type and content ratio of the metal silicide crystal phase contained in the obtained DPF, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and the content ratio of B in terms of B ₂ O _3. Show. Table 4 shows the porosity, strength, and thermal conductivity of the obtained DPF.

(Example 28)
A DPF (Example 28) was obtained in the same manner as in Example 26 except that the honeycomb formed body was fired at 1800 ° C. Table 4 shows the type and content ratio of the metal silicide crystal phase contained in the obtained DPF, the content ratio of SiC, the particle diameter and content ratio of β-SiC, and the content ratio of B in terms of B ₂ O _3. Show. Table 4 shows the porosity, strength, and thermal conductivity of the obtained DPF.

  From the results shown in Tables 2 to 4, metal such as nickel (Ni) was also used in Comparative Example 1 manufactured without using boron (B) and boron (B), but metal such as nickel (Ni) was used. The silicon carbide based porous material of Comparative Example 2 manufactured without using this material has high porosity but low strength and thermal conductivity. For this reason, for example, when used as a constituent material of DPF, the deposited soot is burned. There is a risk of damage due to thermal stress generated during the process. The silicon carbide based porous material of Comparative Example 3 manufactured by adding a small amount of nickel (Ni) has a low thermal conductivity for a low porosity. Therefore, for example, when it is used as a constituent material of DPF, it is deposited. There is a possibility of damage due to thermal stress generated when burning soot. Moreover, although the metal such as nickel (Ni) was used but the silicon carbide based porous material of Comparative Example 4 manufactured without using boron (B) had high porosity, the strength was insufficient. It cannot be said that it is suitable as a constituent material. Although nickel (Ni) and boron (B) were used, the silicon carbide based porous material of Comparative Example 5 having a small amount of boron (B) and Comparative Example 6 having a large amount of boron (B) has low strength, For example, when used as a constituent material of a DPF, there is a possibility that the deposited soot may be damaged due to thermal stress generated when it is burned. In Comparative Example 7 having a blended composition aiming at high porosity by adding a large amount of organic pore former, the porosity was too high and the fired body could not be obtained due to insufficient strength. Although the silicon carbide based porous material of Comparative Example 8 produced using nickel (Ni) and boron (B) and using a large amount of α-SiC has a low porosity, for example, it is used as a constituent material of DPF. If so, problems such as increased pressure loss during exhaust gas permeation occur. On the other hand, the silicon carbide based porous bodies of Examples 1 to 22, the honeycomb structures of Examples 23 to 25, and Example 26 manufactured using metals such as nickel (Ni) and zirconia (Zr) and boron (B). ~ 28 DPF has high porosity, high strength and high thermal conductivity, so it can be expected to exhibit excellent filter characteristics and expect to reduce thermal stress generated when burning deposited soot Can do.

  The silicon carbide based porous material of the present invention is suitable as a material constituting various filters including a diesel exhaust gas purifying filter (DPF).

1 is a perspective view showing an embodiment of a honeycomb structure of the present invention. It is a perspective view which shows other embodiment of the honeycomb structure of this invention. Fig. 3 is an enlarged view of a main part of the honeycomb structure shown in Fig. 2. Fig. 3 is a perspective view of a honeycomb segment constituting the honeycomb structure shown in Fig. 2. It is AA sectional drawing of FIG.

Explanation of symbols

1, 11: honeycomb structure, 2: honeycomb segment, 4: coating material, 5, 15: cell, 6, 16: partition wall, 7: filler, 9: bonding material layer, 10: outer wall.

Claims (15)

A silicon carbide based porous material containing 1 to 35% by mass of metal silicide, 0.1 to 10% by mass of boron (B) in terms of boron oxide (B ₂ O ₃ ), and a porosity of 38 to 80% .   The silicon carbide based porous material according to claim 1, wherein the strength is 10 to 50 MPa.   The silicon carbide based porous material according to claim 1 or 2, wherein all silicon carbide contained as a main component is β-SiC.   The content ratio of the β-SiC with respect to the total of the α-SiC and the β-SiC, which includes α-SiC and β-SiC, is 5% by mass or more and less than 100% by mass. Silicon carbide porous body.   The silicon carbide based porous material according to claim 3 or 4, wherein at least a part of the β-SiC has a particle size of 20 µm or more.   The silicon carbide based porous material according to any one of claims 1 to 5, wherein the metal silicide is nickel silicide.   The silicon carbide based porous material according to any one of claims 1 to 6, wherein the thermal conductivity is 5 to 50 W / mK.   A honeycomb-shaped honeycomb structure comprising a plurality of cells partitioned by partition walls, comprising the silicon carbide based porous material according to any one of claims 1 to 7.   Combining and combining a plurality of honeycomb-shaped segments comprising a plurality of cells partitioned by partition walls, comprising the silicon carbide based porous material according to any one of claims 1 to 7, and the predetermined A honeycomb structure formed by plugging an opening of a cell with one end face of the segment and plugging a remaining opening of the cell with the other end face of the segment.   The honeycomb structure according to claim 8 or 9, which is used as a filter for purifying diesel exhaust gas. A raw material mixture containing metal, silicon, carbon, and boron (B) raw materials is formed into a predetermined shape, degreased, and fired, so that metal silicide is 1 to 35% by mass, and boron (B) is boron oxide (B ₂ O). ₃ ) The manufacturing method of the silicon carbide based porous body which obtains the silicon carbide based porous body which contains 0.1-10 mass% in conversion, respectively, and has a porosity of 38-80%.   The method for producing a silicon carbide based porous material according to claim 11, wherein the raw material mixture further contains an α-SiC raw material.   The method for producing a silicon carbide based porous material according to claim 11 or 12, wherein firing is performed at 1250 to 1800 ° C in an argon (Ar) atmosphere or a vacuum atmosphere.   The said boron (B) raw material is the metal B, The manufacturing method of the silicon carbide based porous body as described in any one of Claims 11-13.   The method for producing a silicon carbide based porous material according to any one of claims 11 to 14, wherein the raw material mixture is formed into a honeycomb shape having a plurality of cells partitioned by partition walls.

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