Preparation method of high-performance cordierite DPF honeycomb ceramic

Abstract

The invention discloses a preparation method of high-performance cordierite DPF honeycomb ceramic, and belongs to the technical field of honeycomb ceramic carrier preparation. The preparation method comprises the following steps: mixing raw materials; kneading mud; performing extrusion molding; drying and shaping; cutting and firing to obtain a cordierite honeycomb ceramic carrier; and performing boundary dimension processing, film covering, hole dotting, mud scraping and drying to obtain a finished product. According to the invention, aluminum hydroxide is adopted to replace or partially replace aluminum oxide in the formula of the cordierite porous ceramic structure while magnesium hydroxide is used, and the two substances can form a synergistic heat absorption mechanism by virtue of the difference of the aluminum hydroxide and magnesium hydroxide in thermal decomposition temperature, so that the heat absorption efficiency of the cordierite porous ceramic structure is greatly improved in the low-temperature coke discharge stage of a carrier mud blank. Aluminum hydroxide is subjected to a decomposition reaction before magnesium hydroxide, and then magnesium hydroxide is continuously decomposed at a higher temperature, so that the temperature range covered by the whole heat absorption process is greatly widened, the heating rate of the carrier mud blank is effectively slowed down, and thermal shock caused by sudden rising of local temperature is avoided.

Description

Technical Field

[0001] This invention belongs to the field of honeycomb ceramic carrier preparation technology, specifically relating to a method for preparing high-performance cordierite DPF honeycomb ceramics. Background Technology

[0002] With increasingly stringent environmental requirements and continuously upgraded vehicle emission standards, the implementation of the China VII emission standard is now on the agenda. Against this backdrop, the technological innovation of the diesel particulate filter (DPF), a key device for controlling diesel engine particulate emissions, is particularly important. The China VII DPF may adopt an asymmetric DPF product with a wall thickness of 7 mil, which is thinner than the China VI asymmetric DPF product. While this design theoretically helps reduce exhaust back pressure and improve engine performance, it presents significant challenges in actual production. Due to the thinner wall thickness, the product is more prone to cracking and failure during the firing stage due to thermal stress concentration, which not only increases production costs but also affects production efficiency and quality stability.

[0003] Currently, the choice of material formulation is crucial in solving the problem of firing cracks in DPF products. Practice has shown that products using an aluminum hydroxide + magnesium hydroxide formulation exhibit higher stability and a higher survival rate during firing. Magnesium hydroxide absorbs a large amount of heat when heated, thus slowing down the heating rate of the carrier clay. Furthermore, during thermal decomposition, it releases bound water, which further absorbs heat and dilutes the oxygen concentration, helping to inhibit rapid heating and thus suppressing the formation of cracks in the clay during firing, thereby improving the yield of fired products. Magnesium hydroxide decomposes into magnesium oxide (MgO), which possesses excellent refractory properties and further slows down the combustion process. Aluminum hydroxide plays a similar role when heated, except for its decomposition temperature. The thermal decomposition temperature of magnesium hydroxide (340-490℃) falls within the coking range of organic pore-forming agents and binders, while the initial thermal decomposition temperature of aluminum hydroxide (200-300℃) misses most of this range. Using aluminum hydroxide alone is not ideal. However, using magnesium hydroxide and aluminum hydroxide together allows for the absorption of a large amount of heat over a wider temperature range, thereby slowing down the heating rate of the carrier clay and the combustion process. This enhances the mechanical properties and thermal stability of the product, effectively resisting thermal stress and reducing the risk of cracking. However, existing research and application of this formulation structure are not yet in-depth or widespread. How to further optimize the formulation ratio, fully utilize its advantages, and better apply this formulation to the production of products that are prone to cracking and sensitive to firing, such as 7 mil thick asymmetric DPF, remain urgent problems to be solved. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing high-performance cordierite DPF honeycomb ceramics. This method has good adaptability to firing regimes and can significantly improve the yield of fired products.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing high-performance cordierite DPF honeycomb ceramics includes the following steps:

[0007] (1) Mix talc, magnesium hydroxide, aluminum oxide, aluminum hydroxide, silicon dioxide and kaolin, then add binder and pore-forming agent and continue mixing, then mix with water;

[0008] (2) The clay is kneaded, coarsely refined, and then refined in a clay kneader to obtain clay material;

[0009] (3) The clay material is extruded in an extruder to form a honeycomb ceramic carrier green body;

[0010] (4) The green body of the honeycomb ceramic carrier is microwave dried and shaped;

[0011] (5) The dried carrier is cut and fired to obtain a cordierite honeycomb ceramic carrier;

[0012] (6) External dimensions processing, film coating, hole punching, mud scraping, drying, finished product.

[0013] Further, in step 1), there are 8.39-41 parts of talc, 5-15 parts of magnesium hydroxide, 12.68-28.5 parts of aluminum oxide, 3-9 parts of aluminum hydroxide, 20.5-40.07 parts of silicon dioxide, 10 parts of kaolin, 6 parts of binder, and 20 parts of pore-forming agent.

[0014] Further, in step (1), the particle size of talc is 5-35 μm, the particle size of magnesium hydroxide is 5-35 μm, the particle size of alumina is 4-9 μm, the particle size of aluminum hydroxide is 2-5 μm, the particle size of silica is 5-35 μm, the particle size of kaolin is 3-8 μm, and the particle size of the pore-forming agent is 10-40 μm.

[0015] Furthermore, in step (1), the binder is hydroxypropyl methylcellulose and the pore-forming agent is starch.

[0016] Furthermore, in step (1), the amount of water added is 20-30% of the total weight of the raw materials.

[0017] Furthermore, in step (2), the coarse sieving uses an 80-mesh sieve, the clay is kneaded for 15-20 minutes, aged for 12-16 hours, and the fine sieving uses a 100-mesh sieve.

[0018] Furthermore, in step (4), the moisture content of the dried honeycomb ceramic carrier green body is less than 1.0%.

[0019] Further, in step (5), the heating rate is 20 ℃ / h for room temperature to 200 ℃; the heating rate is 25 to 50 ℃ / h for 200 to 800 ℃; the heating rate is 45 ℃ / h for 800 to 1410 ℃; and the temperature is maintained at 1410 ℃ for 10h.

[0020] Furthermore, in step (6), the asymmetric DPF product has a diameter of 305 mm, a height of 305 mm, a pore density of 300 mesh, a wall thickness of 7 mil, a large pore diameter of 1.632 ± 0.05 mm, and a small pore diameter of 1.312 ± 0.05 mm.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] (1) This invention uses aluminum hydroxide to replace or partially replace alumina in the cordierite porous ceramic structure formulation while using magnesium hydroxide. Utilizing the difference in thermal decomposition temperatures between aluminum hydroxide and magnesium hydroxide (210 ℃ for aluminum hydroxide and 330 ℃ for magnesium hydroxide), the two substances can form a synergistic endothermic mechanism. During the low-temperature coke removal stage of the carrier clay, aluminum hydroxide decomposes before magnesium hydroxide, and then magnesium hydroxide continues to decompose at higher temperatures, significantly widening the temperature range covered by the entire endothermic process. Compared to a single formulation using only magnesium hydroxide, this stepwise decomposition reaction can absorb more heat, thereby effectively slowing down the heating rate of the carrier clay and avoiding thermal shock caused by sudden local temperature increases.

[0023] (2) The slowing down of the heating rate of the present invention directly optimizes the combustion process inside the clay blank: on the one hand, it can reduce the concentrated heat release intensity when the organic components are burning, and reduce the thermal stress caused by instantaneous high temperature; on the other hand, it can provide sufficient time for the orderly discharge of gas inside the clay blank, avoid microcracks caused by poor gas escape, significantly reduce the risk of cracking in the firing stage, greatly improve the structural integrity and dimensional stability of the product, and ultimately achieve a significant improvement in the firing qualification rate, while laying a solid foundation for durability in subsequent use. Attached Figure Description

[0024] Figure 1 This is a cross-sectional schematic diagram of the asymmetric DPF product of this application;

[0025] Figure 2 This is a schematic diagram of the filter cross-section of the asymmetric DPF product of this application;

[0026] Figure 3 For the asymmetric DPF product of this application Figure 1A magnified view of a portion of the image; in the image, 1 represents the diameter of the large hole, and 2 represents the diameter of the small hole. Detailed Implementation

[0027] The present invention will be further illustrated below with reference to specific embodiments. These embodiments are implemented based on the technical solutions of the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0028] The raw material requirements used in the following examples are shown in Table 1.

[0029] Table 1 Raw Material Specifications

[0030]

[0031] Example 1

[0032] A method for preparing high-performance cordierite DPF honeycomb ceramics includes the following steps:

[0033] (1) Mix talc, magnesium hydroxide, aluminum oxide, aluminum hydroxide, silicon dioxide and kaolin, then add binder and pore-forming agent and continue mixing, then add 22% water (the sum of the weight of inorganic material, binder and pore-forming agent) and continue mixing. The specific amount of each raw material is shown in Table 2.

[0034] (2) Knead the clay in a clay kneader, coarsely refining it (using an 80-mesh sieve) for 15 minutes, age it for 12 hours, and then refine and sieve it (using a 100-mesh sieve) to obtain the clay material;

[0035] (3) The clay material is extruded in an extruder to form a honeycomb ceramic carrier green body;

[0036] (4) The honeycomb ceramic carrier blank is microwave dried and shaped, and the moisture content of the dried honeycomb ceramic carrier blank is less than 1.0% (by weight).

[0037] (5) The dried carrier was cut and fired to obtain a cordierite honeycomb ceramic carrier. The firing temperature control program was as follows: at room temperature to 200 ℃, the corresponding heating rate was 20 ℃ / h; at 200 to 800 ℃, the corresponding heating rate was 25 ℃ / h; at 800 to 1410 ℃, the corresponding heating rate was 45 ℃ / h; and the temperature was maintained at 1410 ℃ for 10 h.

[0038] (6) External dimensions processing, coating, dotting, scraping, drying, finished product. Asymmetric DPF product diameter 305 mm, height 305 mm, pore density 300 mesh, wall thickness 7 mil, large pore diameter 1.632±0.05 mm, small pore diameter 1.312±0.05 mm. (e.g.) Figure 1-3 As shown.

[0039] The specific product formula and product performance test results are shown in Table 2.

[0040]

[0041] Samples of products 1 to 11 in the table above were produced using the same mold, extruder, kiln, and fired in the same kiln. The binder was hydroxypropyl methylcellulose, and the pore-forming agent was starch.

[0042] The median pore size was determined using the mercury intrusion porosimetry method (GB / T 21650.1-2008). Test parameters were set as follows: mercury contact angle 130°; mercury surface tension 0.485 N / m; mercury density (20 ℃) ​​13.5335 g / mL; pressure data were acquired using a step-by-step mode, with a pressure equilibrium time of 10 s; no pretreatment was performed. The thermal shock resistance of the honeycomb ceramics was determined using GB / T 25994-2010. The coefficient of thermal expansion was measured using a thermal dilatometer according to GB / T 7320-2018. Porosity was determined using the buoyancy method according to GB / T 1966-1996.

[0043] As shown in Table 2, the best firing rate of clay blanks was achieved when 10% magnesium hydroxide and 5% aluminum hydroxide were used in the cordierite DPF formulation.

[0044] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for making high performance cordierite DPF honeycomb ceramic, characterized by: The method comprises the following steps: (1) mixing talc, magnesium hydroxide, aluminum oxide, aluminum hydroxide, silicon dioxide and kaolin, then adding a binder and a pore-forming agent for further mixing, and mixing with water; (2) kneading, rough refining and fine refining in a kneading machine to obtain a mud; (3) extruding the mud in an extruder to obtain a green body of the honeycomb ceramic carrier; (4) microwave drying and shaping the green body of the honeycomb ceramic carrier; (5) cutting and sintering the dried carrier to obtain a cordierite honeycomb ceramic carrier; (6) processing the outer dimensions, coating, drilling, mud scraping, drying and finishing.

2. The method for producing high-performance cordierite DPF honeycomb ceramics according to Claim 1, characterized by: In step 1), the talc is 8.39-41 parts, the magnesium hydroxide is 5-15 parts, the aluminum oxide is 12.68-28.5 parts, the aluminum hydroxide is 3-9 parts, the silicon dioxide is 20.5-40.07 parts, the kaolin is 10 parts, the binder is 6 parts, and the pore-forming agent is 20 parts.

3. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (1), the particle size of the talc is 5-35 μm, the particle size of the magnesium hydroxide is 5-35 μm, the particle size of the aluminum oxide is 4-9 μm, the particle size of the aluminum hydroxide is 2-5 μm, the particle size of the silicon dioxide is 5-35 μm, the particle size of the kaolin is 3-8 μm, and the particle size of the pore-forming agent is 10-40 μm.

4. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (1), the binder is hydroxypropyl methylcellulose, and the pore-forming agent is starch.

5. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (1), the amount of water added is 20-30% of the total weight of the raw materials.

6. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (2), the rough refining is sieved through a 80-mesh screen, the kneading is performed for 15-20 minutes, the aging is performed for 12-16 hours, and the fine refining is sieved through a 100-mesh screen.

7. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (4), the weight moisture content of the dried green body of the honeycomb ceramic carrier is less than 1.0%.

8. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (5), the temperature is raised at a rate of 20 ℃ / h from room temperature to 200 ℃, at a rate of 25-50 ℃ / h from 200 to 800 ℃, at a rate of 45 ℃ / h from 800 to 1410 ℃, and the temperature is maintained at 1410 ℃ for 10 h.

9. The method of making high performance cordierite DPF honeycomb ceramic according to claim 1, characterized in that: In step (6), the asymmetric DPF product has a diameter of 305 mm, a height of 305 mm, a pore density of 300 meshes, a wall thickness of 7 mil, a large pore size of 1.632±0.05 mm, and a small pore size of 1.312±0.05 mm.

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