JPH0149666B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a cordierite-based ceramic honeycomb, and more particularly to a method for producing a cordierite-based ceramic honeycomb that has excellent not only thermal shock resistance but also heat resistance, and excellent catalyst-supporting and catalytic properties. A ceramic honeycomb can be defined as a structure made of ceramic material and having a thin-walled cellular shape, ie a honeycomb shape. The cross-sectional shapes of these cells include hexagons, squares, rectangles, triangles,
It can have any geometric pattern, such as a circle. The average pore diameter, which is one of the properties related to the pores in the thin wall surface of ceramic honeycomb, can be defined as the pore diameter corresponding to 50% of the total pore volume in the pore distribution determined by mercury intrusion porosimetry. Ceramic honeycombs are used as catalyst carriers in devices for purifying hydrocarbons, carbon monoxide, and nitrogen oxides from automobile exhaust gas. Ceramic honeycomb catalyst carriers used in these automobile exhaust gas purification devices are required to have several important properties. One of the required properties is so-called thermal shock resistance, which is caused by the temperature difference that occurs within the honeycomb due to the sudden temperature change due to heat generation due to the catalytic oxidation reaction of unburned hydrocarbons and carbon monoxide in the exhaust gas. It has the property of resisting cracking or fracture due to induced thermal stress. This thermal shock resistance is expressed by the durability temperature difference between rapid heating and cooling, and the durability temperature difference is
There is no practical problem if the temperature is 500℃ or higher. It has been found that this rapid heating/quenching durability temperature difference is inversely proportional to the thermal expansion coefficient among the characteristics of the honeycomb, and the smaller the thermal expansion coefficient is, the larger the durability temperature difference is. Another property required of the ceramic honeycomb catalyst support is heat resistance, which means that when raw gas generated by a misfire in an automobile engine flows into the honeycomb catalyst, it will not undergo partial melting or softening changes due to the rapid temperature rise caused by the oxidation reaction. It is. This heat resistance is expressed by softening temperature, melting temperature, and generally softening shrinkage rate at 1450°C, and the higher the softening temperature and melting temperature, and the lower the softening shrinkage rate at 1450°C, the higher the heat resistance. Cars equipped with catalytic purification devices are usually equipped with various safety devices such as a secondary air control mechanism to suppress misfires, so there is no practical problem if the softening shrinkage rate of ceramic honeycomb is 10% or less at 1450°C. It is said that Other properties required of the ceramic honeycomb catalyst carrier are adhesion between the honeycomb catalyst carrier and the catalytically active substance and the catalytic substance. This is the ability to maintain adhesion so that the coating does not peel off during driving. Conventionally, ceramic honeycomb structures have generally been made of ceramics such as cordierite, mullite, alumina, zircon, and lithia.
These include carbides and nitrides. Among these materials, materials such as cordierite, mullite, alumina, and zircon are used for the ceramic honeycomb catalyst carrier for engine exhaust gas purification due to their heat resistance and oxidation resistance. Conventionally used ceramic honeycombs made of mullite, alumina, zircon, and mixtures thereof are superior to cordierite honeycombs in terms of heat resistance, and their high-temperature stability at temperatures of about 1450°C is sufficient for practical use. Because the coefficient of thermal expansion is 3 to 5 times larger than that of cordierite honeycomb, it has excellent thermal shock resistance, and can withstand temperature changes caused by rapid catalytic oxidation exothermic reactions such as unburned hydrocarbons and carbon monoxide in exhaust gas. The drawback was that the large temperature difference that occurred within the honeycomb caused the honeycomb to crack and break. On the other hand, cordierite-based ceramic honeycombs are disclosed in US Pat. 50−
As disclosed in Japanese Patent No. 75612), it exhibits low thermal expansion and has excellent thermal shock resistance, but its melting point is lower than that of mullite honeycomb, alumina honeycomb, etc., and the temperature is usually about 1400℃ or higher. Cordierite honeycomb rapidly softens or melts at temperatures such as 1450℃ due to engine misfire.
When the temperature rises to a certain level, the honeycomb has the disadvantage that it softens and deforms or melts. In addition, for example, the US Patent Specification No. 2 entitled "Catalyst Support" granted to John Johns Benbow et al. on July 16, 1974, which is used as a method for manufacturing honeycomb structures,
Specification No. 3824196 (Special Publication No. 51-1232), Showa
U.S. Patent No. 3,790,654 entitled "Extrusion Method for Forming Thin Walled Honeycomb Structures" awarded to Rodney Day Bagley on February 5, 1974 55960) and its division in 1975.
Ceramic honeycombs made by extrusion as disclosed in U.S. Pat. By high-pressure extrusion molding, the structure becomes denser, the total pore volume becomes smaller, and at the same time, the thin wall, especially the average pore diameter on the surface of the thin wall, becomes smaller, which improves the adhesion retention between the catalyst support and the catalytically active substance and the catalytic substance. The problem was that it deteriorated and peeling easily occurred during use. Furthermore, in the production of extruded honeycombs, when forming plasticized batches into honeycomb shapes, drying, and firing to obtain ceramic honeycombs, fine grain raw materials are used as honeycomb raw materials, or raw materials containing crystallization water, carbonates, sulfuric acid, etc. When raw materials that contain a large amount of salt, such as nitrates, are used, the shrinkage during the drying and calcination processes is large, which tends to cause cracks during the drying and calcination processes, resulting in poor manufacturing yields. It was hot. Ceramic honeycomb catalyst carriers used in automobile exhaust gas purification devices are used under extremely severe conditions, and have excellent thermal shock resistance, heat resistance, and catalytic active substances.
There is a strong demand for ceramic honeycombs that have excellent adhesion to catalyst materials. In the present invention, the main component of the crystal phase is cordierite and at least one type of crystal selected from the group consisting of spinel, mullite, and corundum is used.
It was discovered that by containing cordierite in a weight percent, the softening temperature and melting temperature become higher than that of single cordierite, and the softening and shrinkage curve from the softening temperature to the melting temperature has a gentle slope, which improves heat resistance. This is based on the discovery that the coefficient of thermal expansion is comparable to that of ceramic honeycomb made solely of cordierite, and that the thermal shock resistance is greater. In addition, the present invention has a cordierite composition point (51.3% by weight of silica, 34.9% by weight of alumina and 13.8% by weight of magnesia).
44%) with less silica and more alumina 42-52% by weight silica, 34-48% alumina and 10-18% magnesia, preferably 44-44% silica
By using a chemical composition range of 51% by weight, 35-45% by weight of alumina and 11-16% by weight of magnesia, the main component of the crystalline phase is cordierite and at least one type of crystal selected from the group consisting of spinel, mullite and corundum. It has excellent heat resistance and has a thermal expansion coefficient of 16x.
This is based on the discovery that a ceramic honeycomb with extremely excellent thermal shock resistance of 10 ^-7 (1/℃) or less can be obtained. Furthermore, the present invention is based on the discovery that by setting the average pore diameter to 3 to 30 microns, excellent adhesion between the honeycomb catalyst carrier and the catalytically active substance and the catalytic substance can be achieved. Furthermore, in the present invention, preferably 90%
It is based on the discovery that by introducing ~10% by weight, more preferably 80-20% by weight, it is possible to prevent the occurrence of cracks during the honeycomb manufacturing process. Therefore, the main object of the present invention is to provide a method for producing a cordierite ceramic honeycomb that improves the heat resistance, which was a disadvantage of cordierite, while maintaining the excellent thermal shock resistance of cordierite. Another object of the present invention is to provide a method for producing a cordierite ceramic honeycomb that has excellent adhesion to a catalytically active substance and a catalytic substance when used as a catalyst carrier. Another object of the present invention is to form, dry, and
To provide a method for producing a cordierite ceramic honeycomb that does not cause cracks during the firing process. The present invention has a chemical composition of 42-52% by weight silica, 34-48% by weight alumina and 10-18% by weight magnesia (preferably 44-51% silica, 35% by weight alumina).
~45% by weight and 11-16% by weight of magnesia), a formulation consisting of talc, aluminum hydroxide and/or alumina and clay selected to have 10~
90% by weight (preferably 20 to 80% by weight) and an average particle size of 10 to
90-10% by weight (preferably 80%) of 100 micron (preferably 20-80 micron) cordierite powder
~20% by weight), a step of plasticizing this batch and forming it into a honeycomb shape, a step of drying this molded body, and a step of firing this dry molded body at 1375°C or higher, The final product contains 2 to 15% by weight of at least one crystal selected from the group consisting of spinel, mullite, and corundum, and has a softening shrinkage rate of 10% or less at 1450°C.
Thermal expansion coefficient in temperature range from ℃ to 1000℃ is 16×10 ^-7
(1/°C) or less. A further object of the invention is to provide talc, aluminum hydroxide and/or Prepare a batch consisting of 85-98% by weight of a formulation consisting of alumina and clay and 2-15% by weight of at least one crystal selected from the group consisting of spinel, mullite and alumina with an average particle size of 20-60 microns. process, plasticizing this batch to form it into a honeycomb shape, drying this molded body, and firing this dry molded body at a temperature of 1,375℃ or higher. To provide a method for producing a cordierite ceramic honeycomb having a softening shrinkage rate of 10% or less and a thermal expansion coefficient of 16×10 ^-7 (1/°C) or less in a temperature range of 25°C to 1000°C. A further object of the invention is to provide talc, aluminum hydroxide and/or 10-90% by weight of alumina and clay formulation and an average particle size of 10-90% by weight of this formulation pre-calcined and ground.
100 micron cordierite powder 90-10% by weight
at least one crystal selected from the group consisting of spinel, mullite, and alumina with an average particle size of 20 to 60 microns and a total amount of 85 to 98% by weight.
A step of preparing a batch consisting of a mixture with 15% by weight, a step of plasticizing this batch and forming it into a honeycomb shape, a step of drying this molded body, and a step of firing this dry molded body at a temperature of 1375°C or higher, A method for manufacturing cordierite ceramic honeycomb comprising a process in which the softening shrinkage rate of the final product is 10% or less at 1450°C and the thermal expansion coefficient is 16×10 ^-7 (1/°C) or less in the temperature range of 25°C to 1000°C. It is on offer. Part or all of the talc and part of the clay as raw materials may be replaced with calcined talc and calcined clay, respectively. In the cordierite ceramic honeycomb obtained by the method of the present invention, the main component of the crystalline phase is cordierite, and in addition to this, it contains 2 to 15% by weight of at least one crystal selected from the group consisting of spinel, mullite, and corundum, From 25℃
Thermal expansion coefficient in the temperature range of 1000℃ is 16×10 ^-7
(1/°C) or less, and the average pore diameter is 3 to 30 microns. The ceramic honeycomb obtained by the method of the present invention has high heat resistance because the main component of the crystalline phase is cordierite and contains 2 to 15% by weight of at least one type of crystal selected from the group consisting of spinel, mullite, and corundum. is as described above, but what is particularly noteworthy is that by including at least one type of crystal selected from the group consisting of spinel, mullite, and corundum, the softening temperature, which is a factor of heat resistance, increases. The slope of the softening contraction curve from the softening temperature to the melting temperature becomes gentler, and the melting temperature becomes higher.
As a result, the softening shrinkage rate at 1450°C was less than 10%, providing heat resistance that satisfies practical needs as a ceramic honeycomb catalyst carrier used in automobile exhaust gas purification equipment. The reasons for the limitations in the present invention are as follows. First, 15 crystals of at least one type selected from the group consisting of spinel, mullite and corundum are
The reason for setting it below 15% by weight is that if it exceeds 15% by weight, there will be no problem with the heat resistance of the cordierite ceramic honeycomb, but the coefficient of thermal expansion in the temperature range from 25℃ to 1000℃ will be 16×10 ^-7 (1/ This is because it cannot withstand thermal shock since the temperature exceeds 30°F (°C). The reason why at least one crystal selected from the group consisting of spinel, mullite, and corundum is set at 2% by weight or more is that if the content is less than 2% by weight, the coefficient of thermal expansion of the cordierite ceramic honeycomb will be 16×10 ^-7 (1/℃) or less, but
This is because the thermal shrinkage rate at 1450°C is 10% or more, resulting in poor heat resistance. The thermal expansion coefficient of cordierite ceramic honeycomb in the temperature range from 25℃ to 1000℃ is 16×10 ^-7
(1/℃) or less because the coefficient of thermal expansion is 16×
If it exceeds 10 ^-7 (1/℃), the temperature difference between rapid heating and rapid cooling will deteriorate.
This is because if the temperature is lower than 500°C and it is used as a honeycomb catalyst carrier for an exhaust gas purification device for a long period of time, cracks will form or breakage will occur, making it unbearable for practical use. The reason why the average pore diameter of the cordierite ceramic honeycomb is set to 3 to 30 microns is that if the average pore diameter is less than 3 microns, the adhesion of the catalytically active substance and catalyst substance to the cordierite ceramic honeycomb catalyst carrier is poor; This is because when used as a catalyst in an exhaust gas catalytic purification device, adhesion tends to deteriorate due to mechanical vibrations, thermal shock, etc. and peeling tends to occur. Furthermore, if the average pore diameter exceeds 30 microns, the mechanical strength of the cordierite ceramic honeycomb structure decreases, the specific surface area of the pore surface decreases significantly, and the catalytic activity also decreases. Chemical composition ranges from 42 to 52% by weight silica, alumina
The reason why the composition range is 34 to 48% by weight and magnesia 10 to 18% by weight is that, as mentioned above, the thermal expansion coefficient of the heat-resistant cordierite ceramic honeycomb is 16 × 10 ^-7 ( 1/
℃) or less, and the rapid heating and quenching durability temperature difference, which is an index of thermal shock resistance, is 500℃ or more, and when used for a long period as a honeycomb-shaped catalyst carrier in an exhaust gas purification device,
This is because cracks or breaks do not occur and a region with excellent heat resistance is provided. More than 52% by weight silica or less than 34% by weight alumina or 18% by weight magnesia
This is because if the amount exceeds 10% by weight, the heat resistance will not improve and the object of the present invention will not be met. If it is less than 1, the coefficient of thermal expansion will exceed 16×10 ⁻⁷ (1/° C.) and the thermal shock resistance will deteriorate. In addition, the chemical composition range is 44-51% by weight of silica and 35-45% by weight of alumina.
The reason why the composition range is 11 to 16% by weight of magnesia and magnesia is that, as mentioned above, in this composition range, the main component of the crystalline phase is cordierite, and in addition, at least one member selected from the group consisting of spinel, mullite, and corundum, which improve heat resistance. 2 to 15 crystals
This is because it provides a region including % by weight, has a coefficient of thermal expansion similar to that of a single cordierite material, and has an extremely excellent thermal shock resistance. In the production method of the present invention, the chemical composition is silica 42~
the amount of talc, aluminum hydroxide and/or alumina and clay blend selected to be 52% by weight, 34-48% alumina and 10-18% magnesia, preferably 10-90% by weight; The reason why the amount of pre-calcined and ground cordierite powder in this formulation is preferably 90-10% by weight is that the talc, aluminum hydroxide and/or alumina and clay formulation is less than 10% by weight; If the cordierite powder obtained by pre-calcining and pulverizing the compound exceeds 90% by weight, the plasticity when mixed and made into a clay will be insufficient, and the formability when extruded into a honeycomb shape will be poor. . On the other hand, if the mixture of talc, aluminum hydroxide and/or alumina and clay exceeds 90% by weight or the cordierite powder obtained by pre-calcining and pulverizing this mixture is less than 10% by weight, after honeycomb extrusion, This is because the shrinkage during drying and firing increases, making it easier for cracks to occur during drying and firing, and especially when manufacturing a large honeycomb in one piece, the yield becomes poor.Furthermore, the average pore diameter of the honeycomb after firing is 3 microns. This is because it becomes unsatisfactory. The reason why the particle size of cordierite powder is set to 10 to 100 microns is that if the particle size is less than 10 microns, the average pore diameter of the honeycomb after firing will be less than 3 microns, and the drying and firing shrinkage during honeycomb manufacturing will increase. This is because it becomes less effective as a raw material. In addition, when the particle size of cordierite powder exceeds 100 microns, the average pore diameter exceeds 30 microns, the mechanical strength of the cordierite ceramic honeycomb decreases, and the specific surface area of the pore surface decreases.
This is because the catalyst activity decreases. In another manufacturing method of the present invention, the chemical composition range is 50 to 52% by weight of silica, 34 to 37% by weight of alumina, and 13 to 15% by weight of magnesia. This is because it provides the optimum range of composition to be produced.
Also, talc selected to have this chemical composition,
The total amount of the aluminum hydroxide/or alumina and clay mixture and the cordierite powder obtained by pre-calcining and pulverizing this mixture is 80% by weight.
At least one type of crystal selected from the group consisting of spinel, mullite and alumina.
~15% by weight or less means that the total amount of the blend of talc, aluminum hydroxide and/or alumina and clay and the cordierite powder pre-fired from this blend is less than 80% by weight, or spinel, 15% by weight of at least one type of crystal selected from the group consisting of mullite and alumina
This is because if the temperature exceeds 100°C, the thermal expansion number of the cordierite honeycomb obtained by firing in the temperature range of 25°C to 1000°C becomes so large that it cannot practically withstand thermal shock. In addition, in this manufacturing method, the reason why the average particle size of spinel, mullite, or corundum is set to 20 to 60 microns is that if the particle size is less than 20 microns, it will react and melt with the cordierite glass matrix component during the firing process and retain its high-temperature viscosity. If the thickness exceeds 60 microns, the surface area of spinel, mullite or corundum will become smaller, and the contact area with the cordierite glass matrix will become smaller, reducing the effect of improving high-temperature viscosity. This is because it reduces Next, examples of the present invention will be described. Talc, aluminum hydroxide, alumina, and clay, and if necessary, calcined talc and/or calcined clay were blended as shown in the table so as to have the chemical composition shown in the table. This blend was mixed, further kneaded, and then dried. This dried material was heated to 1375℃ for 5 minutes.
After firing for a period of time, the powder was ground to the average particle size shown in the table to obtain cordierite powder.

【table】

[Table] In Examples 2 to 4 of the present invention and Reference Examples 1 to 3, this cordierite powder and the raw material mixture were mixed in the proportions shown in the table. In Step 4, cordierite powder and the raw material mixture were further mixed with spinel, alumina, or mullite each having an average particle size as shown in the table, and 100 parts by weight of this mixture was mixed with 5 parts by weight of water and starch paste (water content 80% %) was added, thoroughly kneaded with a kneader, and extruded into a honeycomb shape using a vacuum extruder. After drying this molded body, it was fired at 1400° C. for 3 hours to obtain cordierite ceramic honeycombs of Examples 1 to 6 and Reference Examples 1 to 4 of the present invention shown in the table. Quantification of spinel, mullite, and corundum amounts by powder X-ray diffraction for various cordierite ceramic honeycombs shown in the table, from 25℃ to 1000℃
The thermal expansion coefficient in the temperature range of °C, the temperature difference between rapid heating and rapid cooling, the softening shrinkage rate and melting temperature when held at a temperature of 1450 °C for 15 minutes were compared and measured. The results are shown in the table. As is clear from the measurement results in the table, the main component of the crystal phase is cordierite, and in addition, 2 to 15% by weight of at least one type of crystal selected from the group consisting of spinel, mullite, and corundum. The softening shrinkage rate is within 10% and the melting temperature is 1460 when held for minutes.
℃ or higher, so it has sufficient heat resistance for practical use.
Thermal expansion coefficient in the range from 1000℃ to 16×10 ^-7
(1/℃) or less, the rapid heating and cooling durability temperature difference is 500℃ or more, and the thermal shock resistance is practically satisfactory. Furthermore, the batch composition is cordierite powder with an average particle size of 10 to 100 microns. Because it is formulated with
30 microns, and has excellent adhesion between the honeycomb catalyst carrier and the catalytically active substance and catalytic substance. As described above, the cordierite ceramic honeycomb obtained by the method of the present invention has a crystalline phase mainly composed of cordierite and containing 2 to 15% by weight of at least one type of crystal selected from the group consisting of spinel, mullite, and corundum. It has excellent heat resistance and thermal shock resistance, and has an average pore diameter of 3 to 30 microns, so it has excellent catalyst adhesion and is used not only as a catalyst carrier for automobile exhaust gas purification, but also in various types. It can be widely used in industrial catalyst carriers, various heat exchangers, etc., and is extremely useful industrially.

Claims (1)

[Claims] 1. Chemical composition: 42 to 52% by weight silica, 34% alumina
Preparation 10 consisting of talc, aluminum hydroxide and/or alumina and clay selected to be ~48% by weight and 10-18% by weight of magnesia
90% by weight and 90% to 10% by weight of cordierite powder with an average particle size of 10 to 100 microns obtained by pre-calcining and pulverizing this mixture, and plasticizing the batch to form it into a honeycomb shape. a step of drying the molded body,
This dry molded body is fired at 1375°C or higher, and the final product contains 2 to 15 crystals of at least one type selected from the group consisting of spinel, mullite, and corundum.
Including weight%, softening shrinkage rate at 1450℃ less than 10%, 25℃~1000
The coefficient of thermal expansion in the temperature range of ℃ is 16×10 ^-7 (1/℃)
A method for manufacturing cordierite ceramic honeycomb characterized by a combination of the following steps. 2. The method for producing a cordierite ceramic honeycomb according to claim 1, wherein part or all of the talc is replaced with calcined talc. 3. The method for producing a cordierite ceramic honeycomb according to claim 1, wherein a part of the clay is replaced with calcined clay. 4 Chemical composition: silica 50-52% by weight, alumina 34
A formulation consisting of talc, aluminum hydroxide and/or alumina and clay chosen to be ~37% by weight and 13-15% by weight of magnesia85~
98% by weight and 2-15% by weight of at least one crystal selected from the group consisting of spinel, mullite and alumina having an average particle size of 20-60 microns; a process of drying this molded body, and firing this dry molded body at a temperature of 1375°C or higher to reduce the softening shrinkage rate of the final product to 10% or less at 1450°C and 25°C to 1000°C. A method for producing a cordierite ceramic honeycomb characterized by a combination of a process in which the coefficient of thermal expansion is 16×10 ^-7 (1/℃) or less in a temperature range of . 5. The method for producing a cordierite ceramic honeycomb according to claim 4, wherein part or all of the talc is replaced with calcined talc. 6. The method for producing a cordierite ceramic honeycomb according to claim 4, wherein a part of the clay is replaced with calcined clay. 7 Chemical composition: 50-52% by weight of silica, 34% alumina
Preparation 10 consisting of talc, aluminum hydroxide and/or alumina and clay selected to be ~37% by weight and 13-15% by weight of magnesia
90% by weight and 90-10% by weight of cordierite powder with an average particle size of 10-100 microns pre-calcined and ground from this formulation, 85-98% by weight;
preparing a batch consisting of 2-15% by weight of at least one crystal selected from the group consisting of spinel, mullite and alumina having an average particle size of ~60 microns and plasticizing the batch into a honeycomb shape; A process of molding, a process of drying this molded body, and a process of firing this dry molded body at a temperature of 1375°C or higher to reduce the softening shrinkage rate of the final product to 10% or less at 1450°C and within the temperature range of 25°C to 1000°C. Thermal expansion coefficient 16
A method for manufacturing a cordierite ceramic honeycomb characterized by a combination of a process of reducing the temperature to ×10 ^-7 (1/°C) or less. 8. The method for producing a cordierite ceramic honeycomb according to claim 7, wherein part or all of the talc is replaced with calcined talc. 9. The method for producing a cordierite ceramic honeycomb according to claim 7, wherein a part of the clay is replaced with calcined clay.