JP5193805B2 - Silicon carbide based porous material and method for producing the same - Google Patents

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. 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 including a metal silicide in a predetermined ratio, and the present invention is completed. It came.

  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] A silicon carbide based porous material containing 1 to 35% by mass of nickel silicide , a porosity of 38 to 80%, and a pore diameter of 10 to 60 μm.

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

[3] In the above [1], containing 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 described.

[ 4 ] The silicon carbide based porous material according to any one of [1] to [ 3 ], containing 0.5 to 10% by mass of alumina (Al ₂ O ₃ ).

[ 5 ] The silicon carbide based porous material according to any one of [1] to [ 4 ], wherein the thermal conductivity is 1 to 20 W / mK.

[ 6 ] 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 [ 5 ].

[ 7 ] 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 [ 5 ]. 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.

[ 8 ] The honeycomb structure according to [ 6 ] or [ 7 ], which is used as a filter for purifying diesel exhaust gas.

[ 9 ] A raw material mixture containing nickel (Ni) or Ni and aluminum (Al) , silicon and carbon raw material is formed into a predetermined shape, degreased and fired to contain 1 to 35% by mass of nickel silicide , and the porosity Is a method for producing a silicon carbide based porous material that obtains a silicon carbide based porous material having a pore size of 10 to 60 μm.

[ 10 ] The method for producing a silicon carbide based porous material according to [ 9 ], wherein the raw material mixture further includes an α-SiC raw material.

[ 11 ] The method for producing a silicon carbide based porous material according to [ 9 ] or [ 10 ], which is fired at 1250 to 1800 ° C.

[ 12 ] One or more carbon raw materials are used as the carbon raw material, and at least one of them is an average particle diameter selected from the group consisting of amorphous carbon, carbon black granulated particles, activated carbon, and resin carbide. Coarse carbon of 15 to 100 μm, the ratio of the coarse carbon is 10% by mass or more of the total carbon raw material, and the average particle diameter of the coarse carbon is 10 ^× μm, the particle diameter is 10 ^{× The} method for producing a silicon carbide based porous material according to any one of [ 9 ] to [ 11 ], wherein the proportion of the carbon raw material in the range of ^{± 0.25} μm is 70% or more of the total carbon raw material.

[13] The alpha-SiC raw material, the consisting an average particle size of 0.02μm or more 5μm less alpha-SiC raw material (A), the average particle diameter of 5μm or more 100μm following alpha-SiC raw material (B) [10 ] The manufacturing method of the silicon carbide based porous material of description.

[ 14 ] The method for producing a silicon carbide based porous material according to any one of [ 9 ] to [ 13 ], 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 a high porosity while having a high porosity and an atmospheric pore diameter, has a high thermal conductivity, excellent thermal shock resistance, and can be produced by sintering at a relatively low temperature. There is an effect.

  The honeycomb structure of the present invention has an effect that it has a high porosity while having a high porosity and an atmospheric pore diameter, a high thermal conductivity, excellent thermal shock resistance, and can be manufactured by sintering at a relatively low temperature. It is what you play. 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 a high porosity and an atmospheric pore diameter, a high strength, a high thermal conductivity and excellent thermal shock resistance is obtained. It can be easily manufactured by sintering at a low temperature.

  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 a metal silicide, has a porosity of 30 to 80%, and a pore diameter of 10 to 60 μm. 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, when the content ratio of the metal silicide is more than 35% 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.

(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 15% by mass or more, and the upper limit is preferably less than 100% by mass, more preferably 90% by mass or less, and particularly preferably 80% 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. At least a part of the particulate β-SiC is formed by reacting the carbon raw material used in the production of the silicon carbide based porous material of the present invention with silicon, and this β-SiC is the carbon raw material. The particle shape of the carbon raw material is not significantly changed, and the carbon raw material is contained in the silicon carbide based porous material in a state similar to the particle shape of the carbon raw material. Is preferred. When at least a part of β-SiC is contained in such a shape, a silicon carbide based porous material having a high porosity and an air pore diameter is easily obtained.

(alumina)
In the production method described later, when producing the silicon carbide based porous material of the present invention using Al as at least a part of the metal contained in the raw material mixture, Al is oxidized during the firing process, and the silicon carbide based porous material is produced. Alumina (Al ₂ O ₃ ) is formed in the body. Al added as a raw material has the effect of improving the wettability between SiC and silicon (silicon (Si)) or silicide (silicide), which promotes the SiC grain growth in the silicon carbide based porous material. Thus, a structure using SiC with a large particle size as an aggregate is obtained, and a high-strength silicon carbide porous body is obtained.

In the case where Al ₂ O ₃ is contained in the silicon carbide based porous material of the present invention, the lower limit thereof is 0.5% by mass or more when the entire silicon carbide based porous material is 100% by mass. The upper limit is preferably 10% by mass or less, more preferably 9.5% by mass or less, and particularly preferably 8% by mass or less. If the content ratio of Al ₂ O ₃ is less than 0.5% by mass, the amount of Al in the production method cannot be said to be sufficient, and the SiC grain growth promoting effect may be insufficient. On the other hand, when the content ratio of Al ₂ O ₃ is more than 10% by mass, the thermal expansion coefficient of the silicon carbide based porous material may increase.

In the silicon carbide based porous material of the present invention manufactured using a raw material mixture containing Al by a manufacturing method described later, usually, Al ₂ O ₃ is not present in a film form on the surface of SiC particles, It is contained in particulate form. This does not mean that the form itself exhibits any effect, but is one of the characteristics found in the silicon carbide based porous material of the present invention manufactured according to the manufacturing method described later.

(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).

(Pore size)
In the silicon carbide based porous material of the present invention, the pore diameter is 10 μm or more at the lower limit, and 60 μm or less, preferably 55 μm or less, more preferably 50 μm or less, in order to allow gas to permeate efficiently. When the pore diameter is less than 10 μm, the gas permeation coefficient decreases, and the pressure loss that occurs when the gas permeates increases. On the other hand, if the pore diameter exceeds 60 μm, the strength decreases. Such a silicon carbide based porous material having a large pore diameter can be formed, for example, by containing coarse carbon having an average particle diameter of 15 to 100 μm as a carbon raw material in a predetermined ratio in a manufacturing method described later. is there. As used herein, “pore diameter” refers to a value measured with a mercury porosimeter.

(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 1 W / mK or more, more preferably 1.5 W / mK or more, and particularly preferably 2 W / mK or more. Is preferably 20 W / mK or less. When the thermal conductivity is less than 1 W / mK, the thermal shock resistance tends to decrease. On the other hand, when the thermal conductivity is more than 20 W / mK, there is no particular problem, but it is substantially difficult to manufacture.

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 a metal, silicon and a carbon raw material is formed into a predetermined shape, degreased, and fired, so that the metal silicide is 1 to 35% by mass. A silicon carbide based porous material having a porosity of 38 to 80% and a pore diameter of 10 to 60 μm is obtained. 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.

  Moreover, it is also preferable to use Al as a metal in addition to what can produce a metal silicide like nickel (Ni). Al has the effect of improving the wettability between SiC and silicon (silicon (Si)) or silicide (silicide), which makes it easy to obtain a high-strength silicon carbide based porous material.

  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 4 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 diameter of the silicon powder is preferably 1 μm or more, more preferably 3 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 raw material)
The carbon (C) raw material is a component that can generate silicon carbide by reacting with the aforementioned silicon (Si). As the carbon raw material, a powdery (particulate) material is usually used. In the production method of the present invention, one or more carbon raw materials are used as the carbon raw material, and at least one of them is coarse carbon having an average particle diameter of 15 to 100 μm, and the proportion of the coarse carbon is the total carbon. It is preferable that it is 10 mass% or more of a raw material. Thus, when coarse carbon is used as a carbon raw material at a predetermined ratio, formation of ink bottle-shaped pores is avoided, and a large pore diameter of 10 to 60 μm is easily formed, and silicon carbide that can efficiently transmit gas A porous material is obtained. A more preferable average particle diameter of the coarse carbon is 15 to 97 μm, and a more preferable average particle diameter is 15 to 95 μm. Moreover, the more preferable ratio of the said coarse-grained carbon which occupies for all the carbon raw materials is 10-100 mass%, and a still more preferable ratio is 15-100 mass%.

  As the ratio of the coarse carbon increases, the density of the molded body decreases, and the porosity of the obtained fired body (silicon carbide based porous body) tends to increase and the strength decreases, so the strength decreases. In such a case, the strength of the raw material mixture is increased by adding a fine α-SiC raw material to increase the density of the compact or increasing the proportion of the α-SiC raw material in the entire raw material mixture. It is preferable to improve.

When the coarse carbon is used, the ratio of the carbon raw material having a particle diameter in the range of 10 ^{× ± 0.25} μm when the average particle diameter of the coarse carbon is 10 ^× μm, It is preferably 70% or more of the total carbon raw material, more preferably 73% or more, and particularly preferably 75% or more. When the carbon raw material to be used satisfies such conditions, a silicon carbide based porous material having a porosity and a pore diameter defined in the present invention is easily obtained.

  As the coarse-grained carbon, non-crystalline carbon is preferable. For example, at least one carbon raw material selected from the group consisting of amorphous carbon, granulated particles of carbon black, activated carbon, and carbide of resin can be suitably used. Of these, at least one carbon raw material selected from the group consisting of activated carbon and resin carbide is particularly suitable. It is also preferable to use a mixture of a plurality of these, and those less than 15 μm may be used in combination.

(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. In the production method of the present invention, an α-SiC material (A) having an average particle size of 0.02 μm or more and less than 5 μm and an α-SiC material (B) having an average particle size of 5 μm or more and 100 μm or less are used as the α-SiC material. It is preferable to use in combination. As described above, by increasing the proportion of the coarse-grained carbon, when the strength of the finally obtained silicon carbide porous material is too low, a fine α-SiC raw material is added to the compact density. Is an effective means for improving the strength, and thus, as the α-SiC raw material, if two α-SiC raw materials having different average particle diameters are used in combination, It becomes possible to improve the strength by adjusting the proportion of the α-SiC raw material (A) which is fine particles. 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, and α-SiC raw materials described above, examples of the components to be blended in the raw material mixture include organic or inorganic binders, pore formers, surfactants (or dispersants), and water. be able to. 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.

  After drying the molded body, before firing, appropriately calcination (also referred to as degreasing, debinding, etc.) for burning and removing organic substances (binder, dispersant, pore former, etc.) in the molded body It can be carried out. In general, the burning temperature of the organic binder is about 100 to 300 ° C., and the burning 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 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, and has 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.

[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. The NiSi _2, the Ni content obtained by chemical analysis, was calculated value converted into NiSi _2.

  [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.

  [Pore diameter]: Measurement was performed by a mercury intrusion method (based on JIS R 1655) on a sample cut into a size of 6 × 6 × 10 mm.

  [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))
100 parts by mass of a mixture containing 13.4% by mass of nickel (Ni) powder (# 350), 63.8% by mass of silicon (Si) powder (particle size: 78 μm), and 22.8% by mass of carbon (C) powder On the other hand, 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 further added to obtain a raw material mixture. In addition, carbon (a) and carbon (d) shown in Table 1 were used in combination in the carbon powder so that the ratio (ratio) shown in Table 3 was obtained. 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 4, the crystalline 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 27.6% by mass. Moreover, the content rate of (beta) -SiC was 100 mass% when the sum total (total SiC) of (alpha) -SiC and (beta) -SiC was 100 mass%. Furthermore, the porosity was 67%, the pore diameter was 13 μm, and the thermal conductivity was 9 W / mK.

(Examples 2 to 23, Comparative Examples 1 and 2 (Batch Nos. 2 to 25))
Except having set it as the mixing | blending shown in Table 3, it carried out similarly to the case of the above-mentioned Example 1, and obtained the plate-shaped silicon carbide based porous body (Examples 2-23, Comparative Examples 1 and 2). The details of carbon (a) to (d) in Table 3 are shown in Table 1, and the average particle sizes of SiC (a) to (c) are shown in Table 2, respectively. The type and content ratio of the metal silicide crystal phase contained in each of the obtained silicon carbide based porous materials, the content ratio of Al ₂ O ₃ , and the total (total SiC) of α-SiC and β-SiC are 100% by mass. Table 4 shows the content ratio of β-SiC. In addition, Table 4 shows the porosity, pore diameter, and thermal conductivity of each obtained silicon carbide based porous material.

(Example 24)
Batch No. shown in Table 3 An appropriate amount of water was added to the mixture of 3 and 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 about 350 ° C. in an air atmosphere, firing was performed at about 1450 ° C. in an Ar inert atmosphere to obtain a porous honeycomb structure (Example 24). As shown in Table 5, 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 28.4% by mass. Moreover, the content rate of (beta) -SiC was 100 mass% when the sum total (total SiC) of (alpha) -SiC and (beta) -SiC was 100 mass%. Furthermore, the porosity was 63%, the pore diameter was 18 μm, and the thermal conductivity was 8 W / mK.

(Example 25)
Batch No. shown in Table 3 In place of the mixture having the composition of 3, the batch No. A porous honeycomb structure (Example 25) was obtained in the same manner as in Example 24 except that the mixture having the composition of 6 was used. The type and content ratio of the metal silicide crystal phase contained in the obtained honeycomb structure, the content ratio of Al ₂ O ₃ , and the total of α-SiC and β-SiC (total SiC) as 100% by mass Table 5 shows the content ratio of β-SiC. In addition, Table 5 shows the porosity, pore diameter, and thermal conductivity of the obtained honeycomb structure.

(Example 26)
Batch No. shown in Table 1 An appropriate amount of water was added to the mixture of 3 and 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 about 350 ° C. 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 6, 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 28.6% by mass. Moreover, the content rate of (beta) -SiC was 100 mass% when the sum total (total SiC) of (alpha) -SiC and (beta) -SiC was 100 mass%. Furthermore, the porosity was 62%, the pore diameter was 17 μm, and the thermal conductivity was 9 W / mK.

(Example 27)
Batch No. shown in Table 1 In place of the mixture having the composition of 3, the batch No. A DPF (Example 27) was obtained in the same manner as in Example 26 described above, except that the mixture of 6 was used. Table 6 shows the content ratio of β-SiC in the case where the type and content ratio of the metal silicide crystal phase contained in the obtained DPF and the total of α-SiC and β-SiC (total SiC) is 100% by mass. Show. In addition, Table 6 shows the porosity, pore diameter, and thermal conductivity of the obtained honeycomb structure.

  From the results shown in Tables 4 to 6, the silicon carbide based porous materials of Comparative Examples 1 and 2 manufactured without using a metal such as nickel (Ni) have a low porosity, a small pore diameter, and insufficient filter characteristics. It is clear that there is. On the other hand, the silicon carbide based porous bodies of Examples 1 to 23 manufactured using a metal such as nickel (Ni) and aluminum (Al), the honeycomb structures of Examples 24 and 25, and the DPFs of Examples 26 and 27 are as follows. It has been found that it has a high porosity and a large pore diameter, and has excellent filter characteristics. Moreover, since these silicon carbide based porous bodies, honeycomb structures, and DPFs have high thermal conductivity, it is possible to expect a reduction in thermal stress generated when burning the deposited soot.

  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 (14)

A silicon carbide based porous material containing 1 to 35% by mass of nickel silicide, having a porosity of 38 to 80% and a pore diameter of 10 to 60 μm.   The silicon carbide based porous material according to claim 1, wherein all silicon carbide contained as a main component is β-SiC.   2. The silicon carbide according to claim 1, comprising α-SiC and β-SiC, wherein a content ratio of the β-SiC with respect to a total of the α-SiC and the β-SiC is 5% by mass or more and less than 100% by mass. Porous material. The silicon carbide based porous material according to any one of claims 1 to 3 , comprising 0.5 to 10% by mass of alumina (Al ₂ O ₃ ). The silicon carbide based porous material according to any one of claims 1 to 4 , wherein the thermal conductivity is 1 to 20 W / mK. 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 claims 1 to 5 . 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 5 , and 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 6 or 7, which is used as a filter for purifying diesel exhaust gas. A raw material mixture containing nickel (Ni) or Ni and aluminum (Al) , silicon and carbon raw material is formed into a predetermined shape, degreased and fired to contain 1 to 35% by mass of nickel silicide , and a porosity of 38 to 38 A method for producing a silicon carbide based porous material that obtains a silicon carbide based porous material having a pore size of 10 to 60 μm with 80%. The method for producing a silicon carbide based porous material according to claim 9 , 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 9 or 10 , which is fired at 1250 to 1800 ° C. One or more carbon raw materials are used as the carbon raw material, and at least one of them is selected from the group consisting of amorphous carbon, granulated particles of carbon black, activated carbon, and carbide of resin. Coarse carbon, the proportion of the coarse carbon is 10% by mass or more of the total carbon raw material, and the average particle size of the coarse carbon is 10 ^× μm, the particle size is 10 ^{× ± 0. The} method for producing a silicon carbide based porous material according to any one of claims 9 to 11 , wherein a ratio of the carbon raw material in a range of ²⁵ µm is 70% or more of the total carbon raw material. The alpha-SiC raw material, the average and alpha-SiC material of particle size less than 0.02μm or 5 [mu] m (A), consisting of an average particle size of 5 [mu] m or more 100μm following alpha-SiC raw material (B) according to claim 10 according to A method for producing a silicon carbide based porous material. The method for producing a silicon carbide based porous material according to any one of claims 9 to 13 , wherein the raw material mixture is formed into a honeycomb shape having a plurality of cells partitioned by partition walls.

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