JP2009011994A - Ceramic filter and manufacturing method thereof - Google Patents

Abstract

The present invention provides a porous ceramic filter that does not decrease the collection efficiency for PM even after repeated use, and has a small pressure loss of DPF, and has vibration resistance and thermal shock resistance.
A honeycomb filter having a ceramic porous material containing 0.5% by weight or more in a sintered porous ceramic material and a method for manufacturing the same. The ceramic nanotube is preferably a sintered body of a nonmetallic inorganic compound containing at least one element selected from the group consisting of carbon, nitrogen and silicon.
[Selection] Figure 1

Description

  The present invention collects particulates such as carbon and unreacted fuel contained in exhaust gas after combustion of fuel gas in an automobile engine and / or combustion generation of nitrogen oxides and the like in exhaust gas The present invention relates to a ceramic filter for removing an object and purifying exhaust gas.

  Combustion products such as particulate matter (PM) (hereinafter also referred to as “PM”) such as carbon and unreacted fuel and nitrogen oxides in the exhaust gas of gasoline or diesel vehicles are carcinogenic and bronchial asthma. In recent years, exhaust gas emission regulations, including environmental protection, have become stricter.

  As a method for effectively removing PM, generally, a wall flow type diesel particulate filter (DPF) (hereinafter also referred to as “DPF”) is attached to an exhaust gas line after an engine. It has become. This wall flow type DPF has a structure in which the cell hole inlet side and the outlet side of a porous ceramic honeycomb having lattice-type pores are alternately closed. The PM in the exhaust gas flowing into the DPF is collected by the porous ceramic when passing through the cell wall of the porous ceramic. In some cases, using a filter having a honeycomb wall surface coated with a catalyst, PM and exhaust products such as nitrogen oxides in the exhaust gas are simultaneously removed. Currently, cordierite and silicon carbide are generally used as materials for DPF (Non-Patent Document 1).

  In recent years, exhaust gas emission regulations have become stricter, and further improvements in performance of the DPF are required. However, DPF increases the pressure loss of the engine exhaust system and lowers the fuel consumption of the car. Recently, a DPF is placed directly under the engine to collect PM with higher-temperature exhaust gas. So, we are trying to achieve both PM reduction and fuel efficiency. For this reason, heat resistance at higher temperatures and vibrations from the engine are more likely to be placed directly under the engine, and improvements in vibration resistance, thermal shock resistance, and the like are required. In order to reduce the pressure loss, the porosity and pore diameter of the DPF porous ceramics may be increased. However, increasing the porosity leads to a decrease in the strength of the ceramics. There is a trade-off relationship that the ability is reduced (Non-Patent Document 2).

  As another conventional technique, there is a method of filling ceramic spaces or whiskers with 10 vol% or more in a space of a honeycomb structure made of a porous ceramic material used as a DPF (Patent Document 1). In this method, the porous ceramics are sintered into a predetermined shape, and then ceramic whiskers are filled in the pores of the porous ceramics.

Japanese Patent No. 2675071 Akira Okada, “Trends in Structural Ceramics”, Industrial Materials, Nikkan Kogyo Shimbun, August 2005, Vol. 53, No. 8, p.23-27 Shinichi Miwa, “Diesel Exhaust Gas Purification Honeycomb Ceramics”, Industrial Materials, Nikkan Kogyo Shimbun, December 2002, Volume 50, No. 13, p.22-26

  Therefore, in order to improve vibration resistance, thermal shock resistance, etc. more than ever, and to increase PM collection efficiency, porous ceramics having a higher porosity and an appropriate porosity are required. Yes. However, in the conventional method of sintering silicon carbide by adding carbon black or the like, the sintering reaction is performed under the condition that the sintering temperature is increased or the particle size of the raw material powder is reduced in order to increase the sintering density. As a result, the crystal grains after sintering are coarsened, and pores generated after sintering are reduced or reduced, leading to a decrease in porosity and a sufficient effect cannot be obtained.

  In addition, although the collection efficiency and pressure loss are improved by the invention disclosed in Patent Document 1, since it is only filled with ceramic whiskers, when repeatedly used, these whiskers are gradually detached from the ceramics, It may be contained in the exhaust gas. Therefore, at the beginning of filling, the collection efficiency and the pressure loss are surely improved, but the ability is lowered with repeated use. Further, Patent Document 1 discloses 0.5 to 10 μm as the optimum diameter of the whisker. However, whiskers having this diameter are said to be suspected of being carcinogenic as mesothelial species when taken into the alveoli of the human body, which is not preferable for health.

  The present invention has been made in order to solve the above-mentioned problems, and the object of the present invention is to reduce the DPF pressure loss and vibration resistance without reducing the PM collection efficiency even after repeated use. An object of the present invention is to provide a porous ceramic filter having thermal shock resistance.

Said subject was achieved by the following means (1) and (7). They are listed together with preferred embodiments (2) to (6).
(1) A filter comprising a porous ceramic material, wherein the sintered porous ceramic material contains 0.5% by weight or more of ceramic nanotubes,
(2) The filter according to (1), wherein the ceramic nanotube contains at least one element selected from the group consisting of carbon, nitrogen, and silicon,
(3) The filter according to (1) or (2), wherein the ceramic nanotube is at least one nanotube selected from the group consisting of a carbon nanotube, a silicon carbide nanotube, a boron nitride nanotube, and a silicon nitride nanotube,
(4) The filter according to any one of (1) to (3), wherein an average diameter of the ceramic nanotube is 1 μm or less,
(5) The filter according to any one of (1) to (4), wherein the ceramic nanotube has a length of 100 μm or less and has a hollow pipe shape in the length direction,
(6) The filter according to any one of (1) to (5), wherein the filter is a honeycomb filter,
(7) A step of preparing a blend containing ceramic nanotubes, fine powder and a binder and containing 0.5% by weight or more of ceramic nanotubes, a step of molding the blend into a honeycomb-shaped molded body using a molding apparatus, A method for manufacturing a honeycomb filter, comprising: a heating step of heating the molded body to volatilize the binder; and a step of sintering the heated molded body to obtain a honeycomb-shaped sintered body.

According to the filter of the present invention, it is possible to provide a porous ceramic filter having a low DPF pressure loss, vibration resistance, and thermal shock resistance without reducing PM collection efficiency even after repeated use. did it.
Further, according to the filter manufacturing method of the present invention, since the ceramic nanotube is contained, sintering proceeds with the surface of the nanotube as an active site at the time of manufacturing the filter, so that it is not necessary to increase the sintering temperature of the filter. That is, since it is not necessary to increase the sintering temperature of the filter, the sintering density can be increased, and the collecting ability for PM does not decrease. Moreover, the filter itself is reinforced by containing ceramic nanotubes. As a result, a method for producing a filter excellent in vibration resistance and thermal shock resistance could be provided.

The filter of the present invention is a filter made of a porous ceramic material, wherein the sintered porous ceramic material contains 0.5% by weight or more of ceramic nanotubes.
Hereinafter, the filter of the present invention will be described in detail.

<Porous ceramic material>
The filter of the present invention is made of a porous ceramic material. Here, the ceramic material refers to a solid material of a nonmetallic inorganic substance manufactured by heat treatment. The non-metallic inorganic substance is preferably an inorganic compound containing at least one element selected from the group consisting of carbon, nitrogen, and silicon, and includes silicon carbide, silicon nitride, boron carbide, boron nitride, alumina, and cordier. Common materials such as light and mullite can be used, but silicon carbide or cordierite is more preferable, and silicon carbide is particularly preferable because of its excellent thermal conductivity.
Porous means that the porosity is 40% by volume or more. The porosity is preferably 50% by volume or more, more preferably 50 to 80% by volume, and particularly preferably 60 to 80% by volume. Further, the average pore diameter of the porous ceramic material is preferably 20 μm or more, and more preferably 25 to 150 μm.

<Ceramic nanotube>
The filter of the present invention contains ceramic nanotubes. Ceramic nanotubes are hollow, straight ceramic materials with a very thin diameter of several nanometers. Here, the ceramic material is preferably a molded body of an inorganic compound containing at least one element selected from the group consisting of carbon, nitrogen and silicon, and includes silicon carbide, silicon nitride, boron carbide, boron nitride, More preferably, it is a molded body such as alumina. Ceramic nanotubes that can be used in the present invention can contain elements such as boron, aluminum, and titanium as trace components in addition to the main component elements of carbon, nitrogen, and silicon as constituent elements.
The method for producing the ceramic nanotube will be described later.

(Compounding ratio of ceramic nanotube)
The ceramic nanotube is contained in the sintered porous ceramic material by 0.5% by weight or more. Moreover, it is preferable to contain 0.5 to 20 weight%, and it is more preferable to contain 1 to 20 weight%. When the content of the ceramic nanotubes is less than 0.5% by weight, the ceramic nanotubes are arrayed apart regardless of the extrusion direction, and the effect as a reaction catalyst is reduced. When the content is 20% by weight or less, the pores produced by the blending of the ceramic nanotubes are suitable in size, and the impact resistance of the filter is not lowered, which is preferable.

<Method for manufacturing honeycomb filter>
Hereinafter, a method for manufacturing the honeycomb filter of the present invention will be described.
The honeycomb filter of the present invention includes a step of preparing a blend containing ceramic nanotubes, fine powder, and a binder and containing 0.5% by weight or more of ceramic nanotubes, and a honeycomb shaped molded body using the blend with a molding apparatus. And a step of heating the molded body to volatilize the binder, and a step of sintering the molded body after heating to obtain a honeycomb-shaped sintered body.

The description of preferred embodiments of the filter of the present invention will be continued below.
The ceramic nanotube contained in the filter of the present invention is at least one nanotube selected from the group consisting of carbon nanotubes, silicon carbide (SiC) nanotubes, boron nitride (BN) nanotubes, and silicon nitride (Si ₃ N ₄ ) nanotubes. It is preferable. Among these, nanotubes containing silicon carbide are more preferable.
In addition to the above nanotubes, silica (SiO ₂ ), chromium carbide (Cr ₃ C _Z ), lithium aluminosilicate (LiAlSiO _x ), aluminum silicate (AlSiO _x ), aluminum titanate (AlTiO _x ), α-alumina (Al ₂ O ₃₎ ), Nanotubes using a ceramic material such as cordierite can also be used, and these nanotubes can be used alone or in combination of two or more.

(Diameter of ceramic nanotube)
The average diameter of the ceramic nanotubes is preferably 1,000 nm (1 μm) or less. Moreover, it is preferable that it is 10 nm or more, and it is more preferable that it is 10 nm-500 nm. When the average diameter is within the above range, the hollow pipe of the ceramic nanotube is not narrowed, and the ceramic nanotube can be arranged in the extrusion direction at the time of molding. Moreover, since the average diameter of a hollow pipe exists in an appropriate range, the collection capability with respect to PM can be maintained, and the impact resistance of a filter is not reduced.

  The ceramic nanotubes are integrally sintered in a filter made of a porous ceramic material. Therefore, since the ceramic nanotubes are not released from the filter, the nanotubes are not discharged into the exhaust gas. However, even if the released ceramic nanotubes are discharged into the atmosphere, if the average diameter is within the above range, it is thinner than the whisker and has little influence on the human body.

(Length and shape of ceramic nanotube)
The length of the ceramic nanotube is preferably 100 μm or less. Moreover, it is preferable that it is 1 micrometer or more, and it is more preferable that they are 1 micrometer-50 micrometers. When the length is within the above range, pores derived from ceramic nanotubes are appropriate in the filter, and the vibration resistance of the filter does not deteriorate. Further, the pores derived from the ceramic nanotubes are not reduced, and a preferable orientation can be obtained at the time of extrusion molding, so that PM can be efficiently collected.

  The shape of the ceramic nanotube is preferably a hollow pipe shape in the length direction. The ceramic nanotubes are added to the fine powder as a raw material of the filter of the present invention and sintered together. However, the hollow pipes of the ceramic nanotubes remain as pores in the sintered porous ceramic. Therefore, since the filter has an appropriate porosity, there is little pressure loss. In addition, since the hollow pipes of the added ceramic nanotubes tend to be aligned along the extrusion direction in the extrusion process, the orientation of the pores becomes almost constant after sintering, and adjacent pores are fused. Therefore, the pore diameter can be easily controlled without increasing.

  As the ceramic nanotube, a single wall type, a double wall type, and a multi wall type are known. The ceramic nanotubes contained in the filter of the present invention may be any type, but it is preferable to use a multi-wall type from the viewpoint of vibration resistance and thermal shock resistance. Moreover, you may combine these 2 or more types mentioned above.

(Manufacturing method of ceramic nanotube)
Ceramic nanotubes can be produced by reacting carbon nanofibers with silicon oxide, boron oxide or the like, which is a raw material for ceramic materials. Boron nitride nanotubes are produced by a laser heating method under high pressure of nitrogen.
Carbon nanotubes can be produced using various known methods. For example, single-wall nanotubes can be manufactured using graphite with a metal catalyst added and using arc discharge or laser evaporation. Double wall nanotubes can be produced using arc discharge, laser evaporation, hydrocarbon pyrolysis, and the like. The product contains impurities such as amorphous carbon, graphite, nanocapsule fine particles, and metal catalyst, depending on the production method. Impurities are preferably purified and removed. It is preferable to open the end of the closed nanotube using a purification method such as combustion oxidation.
Silicon carbide nanotubes can be produced by reacting multiwall carbon nanofibers with SiO.
Silicon nitride nanotubes can be produced by reacting multi-walled silicon oxide nanofibers at a high temperature in nitrogen.
Boron nitride nanotubes can be produced by reacting multiwall carbon nanofibers with boron oxide in nitrogen.

In Japan, in order to meet the strict diesel emission regulations of local governments, it is virtually required to be a diesel vehicle equipped with a PM reduction device. The PM reduction device includes a DOC (Diesel Oxidation Catalyst), a DPF, or a continuous regeneration DPF system (see US Pat. No. 4,902,487). This continuous regeneration DPF system is a system that uses the strong oxidizing ability of NO ₂ generated by DOC to burn and remove PM trapped in the DPF at a low temperature. It has been reported that a ceramic filter carrying platinum or the like is used in a regenerated DPF system in order to increase the NO ₂ combustion rate. This system is expected to be a continuously regenerating DPF system even under exhaust gas conditions with a low NO _x / PM ratio due to the reoxidation of NO to NO ₂ by a platinum catalyst (Imana Yuki and Kakuya Satoshi, incorporated association) Automobile Engineering Society Academic Lecture Preprints No. 52-07, May 24, 2007 Automotive Engineering Society Spring Academic Lecture Presentation).

(Honeycomb filter)
The filter of the present invention is preferably a honeycomb filter. A wall flow type honeycomb filter is more preferable. A wall flow type honeycomb filter is preferably used as the DPF. Hereinafter, it demonstrates in detail based on drawing.
FIG. 1 is a schematic view showing an end face of one embodiment of a wall flow type honeycomb filter.
As shown in FIG. 1, the cell hole inlet side and the outlet side of a porous ceramic honeycomb having square cell holes are alternately closed. The constituent surface of the square cell hole may be a hexagon.
FIG. 2 is a schematic view showing a cross section of one embodiment of the wall flow type honeycomb filter shown in FIG.
The wall flow type honeycomb filter is provided with a large number of through-holes connected in a honeycomb shape through a porous thin partition wall 2, and one end of the through-hole 1 at a predetermined portion of the hole is sealed with a porous ceramic 3. The other end of the through hole 4 other than the sealed through hole is sealed with a sealing material 5 so that the exhaust gas passes through the partition wall 2. When the exhaust gas passes through the partition wall 2, PM contained in the exhaust gas is collected on the surface of the partition wall 2. PM is also collected in the pores of the ceramic nanotubes oriented along the extrusion direction.
FIG. 3 is a schematic view showing an exhaust gas flow path in an embodiment of the wall flow type honeycomb filter.

The production method of the present invention will be described below using a honeycomb filter containing carbon nanotubes as an example.
As starting materials, contains 98.7 wt% β-type silicon carbide, 1.0 wt% carbon nanotubes, 0.2 wt% oxygen, 0.05 wt% iron, 0.02 wt% boron. The silicon carbide fine powder having an average particle diameter of 0.5 μm is weighed.
A blend in which 10 parts by weight of methyl cellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water are blended with 100 parts by weight of the silicon carbide fine powder is prepared and mixed for 3 hours in a wet ball mill.
Using a metal vacuum extrusion molding apparatus, the silicon carbide fine powder is a circle having an outer diameter of 50 mm and a length of 200 mm at a degree of vacuum of 1,000 Pa or less, an extrusion pressure of 60 kg / cm ² and an extrusion speed of 400 mm / min. A honeycomb-like silicon carbide molded body having a columnar shape, a cell wall thickness of 0.3 mm, and 300 cells is manufactured.
The molded body is dried at 200 ° C., and the dried molded body is heated in the atmosphere in an electric furnace at 400 to 500 ° C., which is a temperature at which silicon carbide itself is not oxidized, and the organic binder and lubricant are volatilized. Let
The molded body after the heat treatment is set in a high-purity graphite crucible, evacuated in a Tamman-type firing furnace, and then replaced with argon gas at 1 atm, and then at 2200 ° C. in an argon atmosphere. A honeycomb filter is obtained by sintering for 8 hours.

Example 1
As starting materials, 98.7% by weight of β-type silicon carbide, 1.0% by weight of carbon nanotubes (manufactured by Shenzhen Nanotechport Co., Ltd .: multiwall nanotubes having a diameter of 80 nm and a length of 10 μm), 0.2% by weight of oxygen, Silicon carbide fine powder containing 0.05 wt% iron and 0.02 wt% boron and having an average particle size of 0.5 μm was weighed.
A blend in which 15 parts by weight of methylcellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water were blended with 100 parts by weight of the silicon carbide fine powder was prepared and mixed for 3 hours by a wet ball mill.
Using an extrusion molding apparatus, a rectangular parallelepiped silicon carbide molded body test piece having a size of 10 mm square and a length of 50 mm was produced from the compound at an extrusion pressure of 100 kg / cm ² . The obtained molded body test piece was dried at 200 ° C. in the atmosphere.
The molded body test piece was heated in nitrogen in an electric furnace at 500 ° C., which is a temperature at which silicon carbide was not oxidized, to volatilize the organic binder and lubricant.
The molded test piece after the heat treatment is set in a high-purity graphite crucible, evacuated in a Tamman-type baking furnace, gas-replaced with 1 atm of argon gas, and then in an argon atmosphere. And sintered at 200 ° C. for 8 hours to produce a sintered body test piece.

The bulk density of the silicon carbide crystal of this sintered body test piece is 2.50 g / cm ³ of porous ceramics. The bending strength at room temperature is 80 kg / mm ² and the bending strength at 1000 ° C. is 75 kg. / Mm ² .

Next, a honeycomb filter was manufactured.
As starting materials, 98.7% by weight of β-type silicon carbide, 1.0% by weight of carbon nanotubes (manufactured by Shenzhen Nanotechport Co., Ltd .: multiwall nanotubes having a diameter of 80 nm and a length of 10 μm), 0.2% by weight of oxygen, Silicon carbide fine powder containing 0.05 wt% iron and 0.02 wt% boron and having an average particle size of 0.5 μm was weighed.
A blend in which 15 parts by weight of methylcellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water were blended with 100 parts by weight of the silicon carbide fine powder was prepared and mixed for 3 hours by a wet ball mill.
Using a metal vacuum extrusion molding apparatus, the blend was formed into a cylindrical shape having an outer diameter of 50 mm and a length of 200 mm at a vacuum degree of 1,000 Pa or less, an extrusion pressure of 60 kg / cm ² , and an extrusion speed of 400 mm / min. A honeycomb-like porous silicon carbide molded body having a cell wall thickness of 0.3 mm and a cell number of 45 / cm ² was produced.
The molded body is dried at 200 ° C., and the dried molded body is heated in nitrogen in an electric furnace at 400 to 500 ° C., which is a temperature at which silicon carbide is not oxidized, to volatilize the organic binder and lubricant. It was.
The molded body after the heat treatment is set in a high-purity graphite crucible, evacuated in a Tamman-type firing furnace, and then replaced with argon gas at 1 atm, and then at 2200 ° C. in an argon atmosphere. The honeycomb filter was obtained by holding for 8 hours and sintering.

(Thermal shock test)
The thermal shock test was performed by installing a honeycomb filter in an electric furnace having a nitrogen valve and an air valve. The nitrogen valve was opened, and the temperature in the furnace was raised to 500 ° C. after the inside of the furnace was under a nitrogen atmosphere. The results of repeating this thermal shock test are shown in Table 1. The thermal shock test is described in “Takahiko Ido, Masafumi Kunieda and Kazumo Ono, Automotive Engineering Society Academic Lecture Preprint No. 52-07, May 24, 2007 Automotive Engineering Society Spring Academic Lecture Presentation”. Can be referred to.

(Underwater quenching test)
In the underwater quenching test, the honeycomb filter was heated to 500 ° C. in the atmosphere and then tested for whether or not cracks would occur by throwing it into water. When there was no crack, it was rated as “◯”, and when it was cracked, it was marked as “X”. The results are shown in Table 1.

(Example 2)
As starting materials, 95.7 wt% β-type silicon carbide, 2.0 wt% α-type silicon carbide, 2.0 wt% silicon carbide nanotubes, 0.2 wt% oxygen, 0.05 wt% A silicon carbide fine powder containing 0.1 wt% aluminum and 0.1 wt% aluminum and having an average particle diameter of 0.5 μm was weighed.
Silicon carbide nanotubes were produced by reacting SiO with multiwall carbon nanofibers having a diameter of 70 nm and a length of 20 μm.
To 100 parts by weight of this silicon carbide fine powder, 15 parts by weight of methyl cellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water were blended and mixed for 3 hours by a wet ball mill.
Using the extrusion molding apparatus, a 10 mm square × 50 mm long rectangular parallelepiped silicon carbide molded body test piece was produced from the mixture at an extrusion pressure of 100 kg / cm ² . The obtained molded body was dried at 200 ° C. in the atmosphere.
The molded body test piece was heated in the air in an electric furnace at 500 ° C., which is a temperature at which silicon carbide is not oxidized, and the organic binder and lubricant were volatilized.
The molded body test piece after the heat treatment is set in a high-purity graphite crucible, evacuated in a Tamman-type firing furnace, and then replaced with argon gas at 1 atm. In an argon atmosphere, Sintered by holding at 2200 ° C. for 8 hours to produce a sintered test piece.

The bulk density of this sintered body test piece is 2.50 g / cm ³ of porous ceramics. The bending strength at room temperature is 95 kg / mm ² , and the bending strength at 1000 ° C. is 85 kg / mm ² . there were.

  Next, a honeycomb filter was manufactured in the same manner as in Example 1. The resulting honeycomb filter was subjected to a thermal shock test and an underwater quenching test in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)
As starting materials, 95.7 wt% β-type silicon carbide, 3.0 wt% α-type silicon carbide, 1.0 wt% boron nitride nanotubes, 0.2 wt% oxygen, 0.05 wt% Silicon carbide fine powder having an average particle diameter of 0.5 μm and containing 0.1 wt% of aluminum and 0.1 wt% of aluminum was weighed.
Boron nitride nanotubes were prepared by reacting boron oxide with nitrogen in multiwall carbon nanofibers having a diameter of 70 nm and a length of 20 μm in nitrogen.
To 100 parts by weight of this silicon carbide fine powder, 15 parts by weight of methyl cellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water were blended and mixed for 3 hours by a wet ball mill.
Using the extrusion molding apparatus, a 10 mm square × 50 mm long rectangular parallelepiped silicon carbide molded body test piece was produced from the mixture at an extrusion pressure of 100 kg / cm ² . The obtained molded body test piece was dried at 200 ° C. in the atmosphere.
The molded body test piece was heated in the atmosphere in an electric furnace at 500 ° C., which is a temperature at which silicon carbide is not oxidized, to volatilize the organic binder.
The molded body test piece after the heat treatment is set in a high-purity graphite crucible, evacuated in a Tamman-type firing furnace, and then replaced with argon gas at 1 atm. In an argon atmosphere, Sintered by holding at 2200 ° C. for 8 hours to produce a sintered test piece.

The bulk density of this sintered body test piece is 2.60 g / cm ³ of porous ceramics. The bending strength at room temperature is 75 kg / mm ² and the bending strength at 1000 ° C. is 70 kg / mm ² . there were.

  Next, a honeycomb filter was manufactured in the same manner as in Example 1. The resulting honeycomb filter was subjected to a thermal shock test and an underwater quenching test in the same manner as in Example 1. The results are shown in Table 1.

Example 4
As starting materials, 95.7 wt% β-type silicon carbide, 3.0 wt% α-type silicon carbide, 1.0 wt% silicon nitride nanotubes, 0.2 wt% oxygen, 0.05 wt% Silicon carbide fine powder having an average particle diameter of 0.5 μm and containing 0.1 wt% of aluminum and 0.1 wt% of aluminum was weighed.
Silicon nitride nanotubes were prepared by reacting multi-wall silicon oxide nanofibers having a diameter of 70 nm and a length of 20 μm in a high temperature of nitrogen.
To 100 parts by weight of this silicon carbide fine powder, 15 parts by weight of methyl cellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water were blended and mixed for 3 hours by a wet ball mill.
Using the extrusion molding apparatus, a 10 mm square × 50 mm long rectangular parallelepiped silicon carbide molded body test piece was produced from the mixture at an extrusion pressure of 100 kg / cm ² . The obtained molded body was dried at 200 ° C. in the atmosphere.
The molded body test piece was heated in the air in an electric furnace at 500 ° C., which is a temperature at which silicon carbide is not oxidized, and the organic binder and lubricant were volatilized.
The heat-treated molded body test piece is set in a high-purity graphite crucible, evacuated in a firing furnace, gas-replaced with 1 atm of argon gas, and then at 2200 ° C. in an argon atmosphere. It was held for 8 hours and sintered to produce a sintered body test piece.

The sintered body test piece has a bulk density of 2.40 g / cm ³ of porous ceramics. The bending strength at room temperature is 70 kg / mm ² , and the bending strength at 1000 ° C. is 60 kg / mm ² . there were.

  Next, a honeycomb filter was manufactured in the same manner as in Example 1. The resulting honeycomb filter was subjected to a thermal shock test and an underwater quenching test in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
As starting materials, 98.7% by weight β-type silicon carbide, 1.0% by weight carbon black, 0.2% by weight oxygen, 0.05% by weight iron, 0.1% by weight aluminum, 0% Silicon carbide fine powder containing 0.02% by weight of boron and having an average particle size of 0.5 μm was weighed.
To 100 parts by weight of this silicon carbide fine powder, 15 parts by weight of methyl cellulose, 3 parts by weight of a glycol lubricant and 300 parts by weight of water were blended and mixed for 3 hours by a wet ball mill.
Using the extrusion molding apparatus, a 10 mm square × 50 mm long rectangular parallelepiped silicon carbide molded body test piece was produced from the mixture at an extrusion pressure of 100 kg / cm ² . The obtained molded body test piece was dried at 200 ° C. in the atmosphere.
The molded body test piece was heated in nitrogen in an electric furnace at 500 ° C., which is a temperature at which silicon carbide was not oxidized, to volatilize the organic binder and lubricant.
The heat-treated molded body test piece is set in a high-purity graphite crucible, evacuated in a firing furnace, gas-replaced with 1 atm of argon gas, and then at 2200 ° C. in an argon atmosphere. It was held for 8 hours and sintered to produce a sintered body test piece.

The bulk density of this sintered body test piece is 2.80 g / cm ³ of porous ceramics. The bending strength at room temperature is 50 kg / mm ² , and the bending strength at 1000 ° C. is 30 kg / mm ² . there were.

  Next, a honeycomb filter was manufactured in the same manner as in Example 1. The resulting honeycomb filter was subjected to a thermal shock test and an underwater quenching test in the same manner as in Example 1. The results are shown in Table 1.

  From the result of this example and the result of the comparative example, in the filter made of a porous ceramic material, the sintered porous ceramic material contains ceramic nanotubes by containing at least 0.5% by weight or more. It was shown that the bulk density was lower than that of the filter without the filter, the bending strength was excellent, and it was able to withstand over 300 thermal shocks. In particular, in Comparative Example 1 that does not satisfy the requirements of the present invention, cracks occurred when the thermal shock was repeated 120 times. In addition, cracking occurred in one rapid quenching in water.

  Based on the above results, a completely new honeycomb filter is manufactured that solves the problems of pressure loss, vibration resistance and thermal shock resistance existing in the conventional manufacturing method while referring to the superior points of the conventional filter. I was able to.

It is a top view which shows the end surface by the side of the exhaust gas of the wall flow type | mold honeycomb filter used by one embodiment of this invention. It is a top view which shows the cross section of the wall flow type honey-comb filter used by one embodiment of this invention. FIG. 3 is a diagram illustrating a flow path of exhaust gas in a wall flow type honeycomb filter used in one embodiment of the present invention.

Explanation of symbols

1, 4 Through hole 2 Partition 3, 5, 5 Porous ceramic sealing material

Claims (7)

  A filter comprising a porous ceramic material, wherein the sintered porous ceramic material contains 0.5% by weight or more of ceramic nanotubes.   The filter according to claim 1, wherein the ceramic nanotube contains at least one element selected from the group consisting of carbon, nitrogen, and silicon.   The filter according to claim 1 or 2, wherein the ceramic nanotube is at least one nanotube selected from the group consisting of a carbon nanotube, a silicon carbide nanotube, a boron nitride nanotube, and a silicon nitride nanotube.   The filter according to claim 1, wherein the ceramic nanotube has an average diameter of 1 μm or less.   The filter according to claim 1, wherein the ceramic nanotube has a length of 100 μm or less and a hollow pipe shape in the length direction.   The filter according to any one of claims 1 to 5, wherein the filter is a honeycomb filter. Preparing a blend comprising ceramic nanotubes, fine powder and a binder and containing 0.5% by weight or more of ceramic nanotubes;
Molding the compound into a honeycomb-shaped molded body using a molding apparatus;
A heating step of heating the molded body to volatilize the binder, and
A method for producing a honeycomb filter, comprising a step of sintering a molded body after heating to obtain a honeycomb-shaped sintered body.

Images