CN111393155A

CN111393155A - Thin-wall large-aperture cordierite honeycomb ceramic carrier and preparation method thereof

Info

Publication number: CN111393155A
Application number: CN202010026103.0A
Authority: CN
Inventors: 牛思浔; 潘吉庆; 张兆合; 黄妃慧; 刘洪月; 程国园; 王勇伟
Original assignee: Chongqing Aofu Fine Ceramics Co ltd
Current assignee: Chongqing Aofu Fine Ceramics Co ltd
Priority date: 2020-01-10
Filing date: 2020-01-10
Publication date: 2020-07-10

Abstract

The invention discloses a thin-wall large-aperture cordierite honeycomb ceramic carrier, wherein the content of cordierite crystalline phase in the cordierite honeycomb ceramic carrier is more than 90%, the median aperture of the cordierite honeycomb ceramic carrier is more than or equal to 4.3 mu m, the porosity is more than or equal to 32.7%, the thermal expansion coefficient is less than or equal to 0.35 × 10-6/DEG C, and the A-axis compression resistance is more than or equal to 5.5 MPa.

Description

Thin-wall large-aperture cordierite honeycomb ceramic carrier and preparation method thereof

Technical Field

The invention relates to a vehicle cordierite honeycomb ceramic body and a preparation method thereof, in particular to a vehicle cordierite product which is thin-walled, large in aperture, low in expansion, high in strength, high in firing qualification rate and beneficial to coating of a catalyst and a preparation method thereof.

Background

In recent years, emission regulations in the automotive industry are continuously upgraded, and the emission of pollutants are more and more strictly limited, so that an aftertreatment system is required to have higher low-temperature conversion efficiency on gaseous pollutants, namely nitrogen oxide (NOx), Hydrocarbon (HC) and carbon monoxide (CO). To achieve good low temperature conversion capability, it is desirable to use thin-walled honeycomb ceramic supports with wall thicknesses of 4 mils, 3 mils, and a lower specific heat capacity of 2 mils.

The production of thin-walled honeycomb ceramic support products requires the reduction of the particle size of the raw material, but the reduction of the particle size, particularly the reduction of the particle size of talc, increases the Coefficient of Thermal Expansion (CTE) of the product (patent CN 108178652A), and for this reason, boehmite is introduced into the raw material, but since boehmite is a submicron or even nano-scale material, the shrinkage of the product is increased, the pore size is reduced to about 1.5 μm, as in the technique disclosed in Japanese patent application No. 2001 and No. 524452, which is not favorable for the coating of the catalyst (generally, the pore size is more than or equal to 3 μm is favorable for the coating. Therefore, in order to increase the pore size of the product, the patent CN100410206C adopts a method of using partially crude alumina to replace boehmite and simultaneously increasing the particle size of kaolin to increase the pore size of the product, and the pore size of the product is at most 4.3 μm. In patent CN 102292309B, about 5-20% of pore-forming agent (corn starch) is introduced to continuously increase the pore diameter of the product, and the median pore diameter is increased to a higher value of 2-10 μm. However, the introduction of the pore-forming agent not only increases the production cost of the product, but also reduces the sintering yield of the product, and the product with large size, such as the product with the diameter of more than or equal to 10.5 inches and the product with the height of more than or equal to 6 inches, can not be sintered.

In addition to the requirement of excellent coating performance of the honeycomb ceramic carrier and the requirement of the honeycomb ceramic carrier to have a low expansion coefficient to cope with the extremely cold and hot environment, the company disclosed in the patent CN 108178652a of the previous application a special preparation method of aluminum hydroxide (hydrolyzed aluminum method) with a particle size D50 of 0.2 μm to 4.0 μm, which can reduce the CTE of the product and the number of microcracks of the product, and can prepare a cordierite honeycomb ceramic article with low CTE, high strength and low cost. But the pore size of the product is smaller by about 2.5-3.0 microns.

Disclosure of Invention

The preparation method can obtain ultrathin walls (2-4mil), large apertures (4-11 mu m) and low expansion (less than or equal to 0.35 × 10)^-6V DEG C), high strength (the compression resistance of an A axis is more than or equal to 5.5MPa), and high firing qualification rate (more than or equal to 98.7 percent).

The invention is realized by the following technical scheme:

a cordierite honeycomb ceramic carrier with thin wall and large pore diameter, the cordierite crystal phase content in the cordierite honeycomb ceramic carrier is more than 90 percent, and the chemical composition of the cordierite honeycomb ceramic carrier is 48.0-52.0 percent of SiO2, 33.8-37.4 percent of Al2O3 and 13.0-15.5 percent of MgO according to mass fraction,

the median pore diameter of the cordierite honeycomb ceramic carrier is more than or equal to 4.3 mu m, the porosity is more than or equal to 32.7 percent, the thermal expansion coefficient is less than or equal to 0.35 × 10-6/DEG C, and the compression resistance of the A axis is more than or equal to 5.5 MPa.

Furthermore, the cordierite crystal phase content in the cordierite honeycomb ceramic carrier is more than or equal to 95 percent, and the chemical compositions of the cordierite honeycomb ceramic carrier comprise 48.0 to 52.0 percent of SiO2, 33.8 to 37.4 percent of Al2O3 and 13.0 to 15.5 percent of MgO according to mass fraction,

the cordierite honeycomb ceramic carrier has a median pore diameter of not less than 5.4 μm, a porosity of not less than 34.1%, and a thermal expansion coefficient of not more than 0.28 × 10^-6/℃，The compression resistance of the A shaft is more than or equal to 8.1 MPa.

The invention also discloses a preparation method of the thin-wall large-aperture cordierite honeycomb ceramic carrier, which comprises the following operation steps:

(1) uniformly dry-mixing an inorganic material and an organic binder to obtain a dry-mixed material; the inorganic material comprises 41.0 to 43 percent of talcum, 3.0 to 21.9 percent of hollow silicon dioxide, 13.7 to 27.8 percent of alumina, 5.0 to 19.62 percent of flaky aluminum hydroxide, 0 to 28.3 percent of inorganic calcined kaolin and 0 to 14.0 percent of raw kaolin according to mass fraction;

(2) adding a surfactant, a lubricant and a dispersant into the dry-mixed materials, and wet-mixing to obtain particles with plasticity;

(3) removing impurities from the plastic particles, and continuously extruding the plastic particles in a vacuum state;

(4) and (3) treating the extruded and molded semi-finished product by using microwave, and simultaneously performing air suction drying, cutting and sintering to obtain the honeycomb ceramic carrier.

The sieving in the preparation method adopts wet sieving, and compared with the traditional dry sieving, the wet sieving has the advantages of less dust, environmental protection, low energy consumption, high efficiency and the like; and the production process adopts air suction drying, which avoids environmental pollution caused by the volatilization of a large amount of low-boiling-point organic matters, fully utilizes microwave exhaust waste heat in the process, reduces heat energy waste, has no process switching from microwave to drying and drying, effectively controls the energy consumption of the honeycomb ceramic blank body in the process of cooling to temperature rise, shortens the process and is beneficial to the improvement of the production efficiency.

Furthermore, the median particle size D50 of the talc is more than or equal to 14 μm, and the maximum particle size D100 is less than or equal to 60 μm;

the adding amount of the hollow silicon dioxide is preferably 3.0-18.0% by mass, the median particle diameter D50 is not less than 16 mu m, the maximum particle diameter D100 is not more than 60 mu m, the bulk density is not more than 0.6g/cm3, and the compressive strength is not less than 20MPa, and the hollow silicon dioxide is prepared by any one of a hollow silicon dioxide template method, a spray drying method and a microemulsion method;

the addition amount of the calcined kaolin is preferably 5.9-22.7% by mass, the median particle size D50 of the calcined kaolin is more than or equal to 6 μm, and the maximum particle size D100 is less than or equal to 35 μm;

the addition amount of the raw kaolin is preferably 0-8.0 percent by mass, the median particle diameter D50 is more than or equal to 14 mu m, and the maximum particle diameter D100 is less than or equal to 60 mu m;

the adding amount of the alumina is preferably 16.2-23.9% by mass, the median particle diameter D50 is more than or equal to 4 μm, and the maximum particle diameter D100 is less than or equal to 25 μm;

the adding amount of the flaky aluminum hydroxide is preferably 5.0-10.0% by mass, the D50 is 0.2-4.0 mu m, the flaky aluminum hydroxide is prepared by an aluminum hydrolysis method, and the specific operation is as follows: using a liquid nitrogen rapid cooling method, at 10⁶-10⁷During the extremely cold process of K/S, a large number of vacancy, dislocation and fault defects are generated on the surface of the metal aluminum, the activity of the metal aluminum is increased, and after the metal aluminum reacts with water, flaky, high-activity, high-purity and high-surface-area aluminum hydroxide is generated, wherein the total mass content of potassium and sodium elements in a finished product is lower than 0.1%.

Furthermore, the median particle diameter D50 of the talc is preferably not less than 16 μm, and the maximum particle diameter D100 of the talc is preferably not more than 50 μm;

the adding amount of the hollow silicon dioxide is more preferably 6-15% by mass, the median particle diameter D50 is preferably more than or equal to 18 microns, the maximum particle diameter D100 is preferably less than or equal to 50 microns, the bulk density is preferably less than or equal to 0.5g/cm3, the compressive strength is preferably more than or equal to 30MPa, and the hollow silicon dioxide is prepared by any one of a hollow silicon dioxide template method, a spray drying method and a microemulsion method;

the median particle size D50 of the calcined kaolin is preferably more than or equal to 8 mu m, and the maximum particle size D100 of the calcined kaolin is preferably less than or equal to 30 mu m;

the adding amount of the raw kaolin is preferably 0-8% by mass, the median particle size D50 is more than or equal to 16 μm, and the maximum particle size D100 is less than or equal to 50 μm;

the median particle size D50 of the alumina is preferably more than or equal to 6 mu m, and the maximum particle size D100 of the alumina is preferably less than or equal to 20 mu m;

the D50 of the flake aluminum hydroxide is preferably 1.0 to 3.0. mu.m.

Further, the organic binder is any one or combination of methylcellulose, hydroxypropyl cellulose and methylcellulose derivatives; the addition amount is 1-10% of the dry-mixed material, and the preferred addition amount is 4-7% of the dry-mixed material.

Further, the surfactant is any one of stearic acid, magnesium stearate, aluminum stearate, lauric acid and oleic acid, and the adding amount of the surfactant is 0.5-6% of the mass of the dry-mixed material, and preferably 1-3% of the mass of the dry-mixed material.

Further, the lubricant is any one of vegetable oil or mineral oil, and the adding amount of the lubricant is 0.5-3% of the mass of the dry-mixed materials, and the adding amount of the lubricant is preferably 1-3% of the mass of the dry-mixed materials.

Further, the dispersant is any one of water or organic dispersant, the organic dispersant is any one of ethanol and acetone, and the adding amount of the organic dispersant is 20-35% of the dry-mixed material by mass, and the adding amount of the organic dispersant is preferably 22-28%.

According to the technical scheme, the beneficial effects of the invention are as follows:

the method has the advantages that the grain size grading of the raw materials is optimized, the raw materials with larger median grain size and the maximum grain size are controlled, for example, calcined kaolin, raw kaolin and alumina with larger median grain size are selected, and the maximum grain size of the raw materials is controlled not to exceed the groove width of the die; meanwhile, spherical hollow silicon dioxide is introduced, the median particle size of the spherical hollow silicon dioxide is larger, the maximum particle size does not exceed the groove width of a mold, the stacking density of the spherical hollow silicon dioxide is smaller than that of solid silicon dioxide, the compressive strength of the spherical hollow silicon dioxide can withstand the pressure of sieving and continuous extrusion, deformation and crushing do not occur in the production process, raw materials with larger median particle sizes are optimized, the stacking pores and the pore sizes in cordierite precursor blanks can be increased, meanwhile, the shrinkage of products can be reduced in the sintering process, the pore sizes of the products are improved, and the defects of broken ribs and the like in the product forming process can be reduced by controlling the maximum particle size of the raw materials to be less than or equal to 50 mu m; by introducing spherical hollow silica, the stacking density of cordierite precursor blanks can be reduced, stacking pores are increased, and in the process of forming cordierite, the pore diameter left in a green body after the hollow spheres react is larger, so that the pore diameter of a product is increased; in the prior patent, pore-forming agents such as pea starch are used to increase the porosity and the pore diameter of the product, but the low-temperature rapid oxidation of the organic pore-forming agents can cause the temperature difference between the inside and the outside of a green body, the oxidation temperature of the organic pore-forming agent is often overlapped with the organic matters such as the binder, the surfactant and the like in the precursor blank, the temperature difference is increased, the thermal stress formed by the large temperature difference can cause the product to crack at the low-temperature stage, the sintering qualification rate is reduced, generally, the heating rate of the product at the low-temperature stage can be reduced when the product is sintered to be qualified, thereby increasing the production period of the product and reducing the production efficiency, the invention uses the inorganic silicon dioxide hollow spheres to replace the organic pore-forming agent, the material can not be oxidized at a low-temperature stage to release heat, the reaction temperature is higher than the oxidation temperature of a binder, a lubricant and the like in a precursor blank, the thermal stress of the blank at the low-temperature stage is reduced, and the qualification rate of products is improved; the hollow microspheres can be organic polymer hollow microspheres and inorganic hollow silica microspheres, but compared with the organic hollow microspheres, the inorganic hollow silica microspheres are generally higher in strength, can bear higher pressure in the processing processes of vacuumizing, extruding and the like, cannot deform and break, so that the parameters of the product such as pore diameter, porosity and the like are more stable, the firing yield is improved, in addition, the hollow silica can be used as a raw material for forming cordierite, is a framework of a precursor blank, and is more cost-saving compared with the organic hollow microspheres.

Drawings

FIG. 1 is a flow chart of the preparation of a thin-walled large-pore-size cordierite honeycomb ceramic carrier;

FIG. 2 shows the variation of pore size, porosity and compressive strength of the ceramic carrier with the addition of hollow silica;

FIG. 3 is a photograph of a pore distribution of a cordierite honeycomb article;

fig. 4 is a surface scan of a cordierite honeycomb article.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The pore size and porosity of the invention are determined by mercury intrusion porosimetry, an instrument is AUTOPORE 9500 manufactured by macmertirek (shanghai) instruments ltd. The median pore diameter D50 of the product is the corresponding pore diameter at which 50% by volume of mercury is pressed into the material pores.

The particle size of the starting material used is the median particle size of the cumulative distribution of the starting material, determined by the principle of laser diffraction, using the eumech instrument L S-609.

The invention discloses a preparation method of a thin-wall large-aperture cordierite honeycomb ceramic carrier, which comprises the following operation steps:

(3) removing impurities from the plastic particles, and continuously extruding under a vacuum state, wherein the diameter of the extruded honeycomb ceramic is less than or equal to 330.2mm, the height of the honeycomb ceramic is less than or equal to 254mm, the mesh number of the product is 900 meshes, and the wall thickness of the product is 2-4 mil;

(4) and (3) treating the extruded and molded semi-finished product by using microwaves, and simultaneously performing air suction drying, cutting and sintering to obtain the honeycomb ceramic carrier, wherein the temperature rising system of the sintering is shown in table 1.

TABLE 1 temperature raising system for firing honeycomb ceramic carrier

Temperature section, temperature	Each period of time (h)	Rate (. degree. C/h)
			Room temperature-500 deg.c	60.0	7.5
500-550	2.0	25.0
			550-600	1.8	28.0
600-1050	11.3	40.0
			1050-1150	2.0	50.0
1150-1270	1.5	80.0
			1270-1370	1.3	76.9
1370-1430	2.0	30.0
			1430-1430	8.0	0.0

the D50 of the flake aluminum hydroxide is preferably 1.0 to 3.0. mu.m.

The raw materials and proportions of the examples of the present invention are shown in Table 2, and the raw materials and proportions of the comparative examples of the present invention are shown in Table 3, wherein in the preparation of the cordierite honeycomb ceramic article of comparative example C4, the pore-forming agent, pea starch, was added to the inorganic material along with the organic binder in step (1) and mixed uniformly, and the remaining preparation methods were completely the same as those of the examples of the present invention.

TABLE 2 inorganic material proportioning table in each example

TABLE 3 proportioning table of inorganic and medium materials in various proportions

The properties of the honeycomb ceramic articles prepared in each of the examples and comparative examples are shown in table 4:

TABLE 4 Properties of the honeycomb ceramic articles prepared in the examples and comparative examples

Comparative example C3, examples E1 to E6 are sequential increases in the amount of hollow silica, and the results show that the pore size and porosity of the product increase with the amount of hollow silica added, but the compressive strength of the product decreases, E2 to E5, which is preferred as a 900 mesh 2mil product, is used in an amount of 3 to 21.9%, preferably 3 to 18%, more preferably 6 to 15%, in view of coating properties and strength of the product, when the resulting product has a pore size of 5.4 to 7.9nm, a porosity of 34.1 to 38.3%, and a CTE of 0.21 to 0.35 × 10^-6The compression strength is 8.1-11.3 MPa. The sintering qualification rate is more than or equal to 99.1 percent. The remaining embodiments can also be used to make carriers or filters.

Comparative example C1 is a comparative example in which no hollow silica was introduced, and the pore diameter of the product was 3.0 μm when no hollow silica was introduced, which was smaller than that of the example; example C2 is a spherical solid silica incorporated with an increase in pore size to 3.6 μm, still smaller than the pore size of the article in the example. A comparison of these two comparative examples with examples E1 to E9 shows that the invention entails the incorporation of hollow silica. Comparative examples C5-C7 are the fine particle calcined kaolin, the fine particle raw kaolin and the fine particle alumina, respectively, in place of the large median diameter calcined kaolin, the raw kaolin and the alumina of example E3. The results show a decrease in median pore size of < 4 μm. Products having median particle sizes of 4 to 10 μm can also be obtained by removing the calcined kaolin of large median particle size or replacing the raw kaolin with alumina of large particle size, as in examples E7, E8 and E9. In summary, hollow silica plus large particle size alumina or calcined kaolin, raw kaolin, formed articles with median pore sizes in the range of 4 to 10 μm. Comparative example C3 was previously invented by the same company using fine non-spherical silica, fine kaolin and fine alumina, the pore size of the product was only 2.9 μm, C4 was that by adding 8% pea starch with a median particle size of 25 μm based on C3, the pore size could be increased to 4.6 μm, but the burn yield of the product would be reduced to 76.5% and would not be within the scope of the present invention.

FIG. 2 shows the pore distribution of the articles of examples E3 and E9 according to the invention shifted towards larger pore sizes compared with comparative example C3; example E3 the article made with the addition of 9% hollow silica and the use of large median diameter calcined kaolin, raw kaolin and alumina and comparative example C4 with the addition of 8% starch but with the use of fine particle calcined kaolin, raw kaolin and alumina gives a cordierite article with a similar pore distribution. FIG. 3 shows that comparative example C3 the surface of the product of the invention made by the present company using fine particle calcined kaolin, raw kaolin and alumina has smaller pores, and the addition of hollow silica in example E3 and the use of large and medium particle size calcined kaolin, raw kaolin and alumina products has significantly larger surface pores similar to the result of the addition of 8% pea starch pore former in comparative example C4, and the addition of 21.9% hollow silica in example E9 has larger surface pores.

The embodiments described above are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Claims

1. The cordierite honeycomb ceramic carrier with thin wall and large pore diameter is characterized in that the content of cordierite crystal phase in the cordierite honeycomb ceramic carrier is more than 90%, and the chemical composition of the cordierite honeycomb ceramic carrier is 48.0-52.0% of SiO in mass fraction₂33.8-37.4% of Al₂O₃13.0 to 15.5 percent of MgO,

the cordierite honeycomb ceramic carrier has a median pore diameter of not less than 4.3 μm, a porosity of not less than 32.7%, and a thermal expansion coefficient of not more than 0.35 × 10^-6The compression resistance of the A axis is more than or equal to 5.5MPa at the temperature of/° C.

2. The cordierite honeycomb ceramic carrier with thin wall and large pore diameter as claimed in claim 1, wherein the cordierite crystal phase content of the cordierite honeycomb ceramic carrier is not less than 95%, and the chemical composition thereof is 48.0-52.0% of SiO2, 33.8-37.4% of Al2O3, 13.0-15.5% of MgO by mass fraction,

the cordierite honeycomb ceramic carrier has a median pore diameter of not less than 5.4 μm, a porosity of not less than 34.1%, and/or a thermal expansion coefficient of not more than 0.28 × 10^-6The pressure resistance of the A axis is more than or equal to 8.1 MPa.

3. A method for producing a thin-walled large-pore cordierite honeycomb ceramic carrier in accordance with claim 1, comprising the steps of:

4. The method of producing a thin-walled large-pore cordierite honeycomb ceramic carrier according to claim 3,

the median particle size D50 of the talc is more than or equal to 14 mu m, and the maximum particle size D100 of the talc is less than or equal to 60 mu m;

the adding amount of the hollow silicon dioxide is preferably 3.0-18.0% by weight, the median particle diameter D50 is more than or equal to 16 mu m, the maximum particle diameter D100 is less than or equal to 60 mu m, and the bulk density is less than or equal to 0.6g/cm³The compression strength is more than or equal to 20MPa, and the hollow silicon dioxide is prepared by any one of a template method, a spray drying method and a microemulsion method;

5. The method of producing a thin-walled large-pore cordierite honeycomb ceramic carrier according to claim 3,

the median particle size D50 of the talc is preferably more than or equal to 16 mu m, and the maximum particle size D100 of the talc is preferably less than or equal to 50 mu m;

the adding amount of the hollow silicon dioxide is more preferably 6-15% by weight, the median particle diameter D50 is preferably more than or equal to 18 mu m, the maximum particle diameter D100 is preferably less than or equal to 50 mu m, and the bulk density is preferably less than or equal to 0.5g/cm³The compressive strength is preferably more than or equal to 30MPa, and the hollow silicon dioxide is prepared by any one of a hollow silicon dioxide template method, a spray drying method and a microemulsion method;

the D50 of the flake aluminum hydroxide is preferably 1.0 to 3.0. mu.m.

6. The method for preparing a thin-walled large-pore cordierite honeycomb ceramic carrier according to claim 3, wherein the organic binder is any one or a combination of methylcellulose, hydroxypropylcellulose and methylcellulose derivatives; the addition amount is 1-10% of the dry-mixed material, and the preferred addition amount is 4-7% of the dry-mixed material.

7. The method for preparing a thin-walled large-pore cordierite honeycomb ceramic carrier in accordance with claim 3, wherein the surfactant is any one of stearic acid, magnesium stearate, aluminum stearate, lauric acid and oleic acid, and is added in an amount of 0.5-6% by mass, preferably 1-3% by mass, of the dry-mixed material.

8. The method for preparing a thin-walled large-pore cordierite honeycomb ceramic carrier according to claim 3, wherein the lubricant is any one of vegetable oil or mineral oil, and is added in an amount of 0.5 to 3% by mass of the dry-mixed material, preferably 1 to 3% by mass of the dry-mixed material.

9. The method for preparing a thin-walled large-pore-size cordierite honeycomb ceramic carrier according to claim 3, wherein the dispersant is any one of water or an organic dispersant, the organic dispersant is any one of ethanol and acetone, and the addition amount of the organic dispersant is 20-35% of the mass of the dry-mixed material, and the preferable addition amount is 22-28%.