Whisker reinforced composite porous ceramic material as well as preparation method and application thereof

Abstract

The invention discloses a whisker-reinforced composite porous ceramic material as well as a preparation method and application thereof, which are based on a new process of combining silicon carbide and cordierite and are combined with factors such as silicon carbide particle size and sintering conditions to really realize effective combination of low thermal expansion characteristic of cordierite and high strength characteristic of silicon carbide. The invention aims to synchronously improve the thermal shock resistance and mechanical bearing capacity of a product so as to provide a DPF filter body material with better performance. Furthermore, in order to optimize the filtering performance, mullite whiskers grow in the composite matrix in situ, and a more efficient particulate matter trapping network is constructed, so that the mechanical reliability, the thermal stability and the filtering efficiency are synergistically improved.

Description

Technical Field

[0001] This invention belongs to the field of porous honeycomb ceramic filter technology, specifically relating to a whisker-reinforced composite porous ceramic material, its preparation method, and its application. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Diesel particulate filters (DPFs) are key aftertreatment devices for reducing particulate matter emissions from exhaust gases, and the overall performance of their filter media directly affects the reliability and service life of the filter. Currently, porous ceramic materials are commonly used as the matrix material for DPFs. Materials used to prepare wall-flow honeycomb ceramic filter media include silicon carbide (SiC), cordierite (2MgO·2Al2O3·5SiO2), aluminum titanate (Al2O3·TiO2), and mullite (3Al2O3·2SiO2). Currently, commercially available DPF filter media primarily use cordierite and silicon carbide.

[0004] Cordierite has a low coefficient of thermal expansion and excellent thermal shock resistance, thus effectively coping with the thermal stress impact caused by drastic fluctuations in diesel engine exhaust temperature. However, its mechanical strength is relatively insufficient, posing a structural risk under mechanical vibration or high-temperature loads.

[0005] The prior art (CN119118640A) discloses a cordierite carrier and its preparation method. The cordierite carrier is obtained by mixing, drying and sintering raw materials. Although the method synthesizes a carrier with a low coefficient of expansion, the material itself has poor mechanical properties and low porosity, making it difficult to use for a long time in its working environment.

[0006] In contrast, silicon carbide exhibits excellent mechanical strength, oxidation resistance, and wear resistance due to its strong covalent bond characteristics. However, its high coefficient of thermal expansion results in insufficient thermal shock resistance, and the requirements for the packaging structure in applications are extremely stringent, increasing the complexity and cost of the process.

[0007] The prior art (CN120554139A) discloses a method for in-situ synthesis of silicon carbide particle traps, which prepares the filter body by reacting metallic silicon powder with graphite powder. Although this method can obtain high-strength silicon carbide monomers, the high thermal expansion characteristics of the material itself are not fundamentally improved, and the thermal shock resistance still faces challenges; at the same time, the dense sintered body has limitations in maintaining sufficient porosity to balance filtration efficiency and back pressure.

[0008] To balance low thermal expansion and high mechanical properties, researchers combined silicon carbide and cordierite to prepare porous ceramics. Li Dan, in her master's thesis "Research on Cordierite-Combined Silicon Carbide Porous Ceramics," explored the effects of cordierite content and different silicon carbide particle sizes on properties including flexural strength, porosity, and shrinkage. However, the product exhibited poor acid resistance. Furthermore, the low cordierite content indicates that the thermal expansion properties of the product were not studied.

[0009] The incorporation of mullite fibers into ceramic matrix materials to improve the mechanical properties of ceramics has long been a research hotspot. Existing technology (CN103601480A) provides a method for preparing a filter body for capturing particulate matter in diesel engines, including the following steps: cordierite, silicon carbide, and ultrafine mullite are mixed uniformly; pore-forming agents, binders, plasticizers, and deionized water are added as auxiliary materials; the mixture is then mixed, kneaded, shaped, microwave-dried, subjected to a special sealing process, and sintered at high temperature to obtain the filter body. The resulting filter body has a softening temperature ≥1510 ℃ and does not crack after three rapid temperature changes at 600 ℃. The honeycomb carrier prepared by this technology exhibits good high-temperature resistance and thermal shock resistance, with a softening temperature ≥1510 ℃ and no cracking after three rapid temperature changes at 600 ℃. However, the sintering temperature of this technical solution is as high as 1450 ℃, resulting in high production costs; secondly, the filter body has a limited number of thermal shock cycles, making it difficult to achieve multiple reuses of the material, thus restricting its application in large-scale industrial production. Summary of the Invention

[0010] To address the limitations of existing technologies, this invention proposes a whisker-reinforced composite porous ceramic material, its preparation method, and its applications. Based on a novel process combining silicon carbide and cordierite, it effectively combines the low thermal expansion characteristics of cordierite with the high strength of silicon carbide, aiming to simultaneously improve the product's thermal shock resistance and mechanical load-bearing capacity, thus providing a higher-performance DPF filter material. Furthermore, to optimize filtration performance, this invention grows mullite whiskers in situ within the composite matrix, constructing a more efficient particulate matter capture network, thereby achieving synergistic improvements in mechanical reliability, thermal stability, and filtration efficiency.

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] In a first aspect, the present invention provides a whisker-reinforced composite porous ceramic material, comprising cordierite / silicon carbide composite honeycomb ceramic as a matrix and mullite whiskers in the matrix; the cordierite / silicon carbide composite honeycomb ceramic uses cordierite powder and silicon carbide powder as main raw materials, hydroxypropyl methylcellulose (HPMC) as plasticizer, carbon powder as pore-forming agent, titanium dioxide as sintering aid, glycerin as lubricant, polyvinyl alcohol (PVA) solution and deionized water are added and uniformly mixed, and after refining and aging, it is extruded with a honeycomb mold, dried, and obtained by reaction sintering.

[0013] Secondly, the present invention provides a method for preparing a whisker-reinforced composite porous ceramic material. First, using cordierite powder and silicon carbide powder as the main raw materials, a composite porous honeycomb ceramic material is obtained by reaction sintering. Then, a vapor phase growth method is used to reinforce the surface of the composite porous honeycomb ceramic material by impregnating it with an impregnation liquid to provide the Si and Al sources required for the synthesis of mullite whiskers.

[0014] In some embodiments of the present invention, the preparation method includes the following steps: Step 1, Preparation of cordierite / silicon carbide composite honeycomb ceramics: Mix 20-80 wt.% cordierite powder, 20-80 wt.% silicon carbide powder, and 0-15 wt.% carbon powder; wherein the particle size of the silicon carbide powder is 200-500 mesh; add titanium dioxide as a sintering aid, polyvinyl alcohol aqueous solution as a binder, add hydroxypropyl methylcellulose, deionized water, and glycerin, mix, knead into a paste, age, extrude into shape, and sinter to obtain the final product; Step 2: Mullite whiskers are generated in situ from the cordierite / silicon carbide composite honeycomb ceramic prepared in Step 1.

[0015] In some embodiments of the present invention, in step 1, 0-9 wt.% titanium dioxide, 0.27-0.33 wt.% polyvinyl alcohol, 7-9 wt.% hydroxypropyl methylcellulose, 29-35 wt.% deionized water and 4.5-5.5 wt.% glycerol are added relative to the content of cordierite and silicon carbide powder.

[0016] In some embodiments of the present invention, the polyvinyl alcohol is added in the form of a 6% aqueous solution, and the amount added is 4.5-5.5 wt.%.

[0017] In some embodiments of the present invention, in step 1, cordierite powder, silicon carbide powder and carbon powder are mixed in a mixer for 0.5-2 h to ensure uniform distribution.

[0018] In some embodiments of the present invention, step 1 includes the following steps: Step 101: Mix the materials according to the required proportions; Step 102: The mixed raw materials are subjected to ordinary mud refining and vacuum mud refining; Step 103: Seal and age the mud block obtained in step 102 for 44-52 hours; Step 104: Use a ceramic extrusion molding equipment to extrude the clay block obtained in step 103 into a mold and then age it for 44-52 hours. Step 105: Sinter and hold for 2-4 hours with a heating program of room temperature ~ 400 ℃: 4 ℃ / min; 400~1000 ℃: 3 ℃ / min; 1000~1150 ℃: 2 ℃ / min.

[0019] In step 2, silica sol, aluminum nitrate solution, and ammonium fluoride solution are prepared respectively. The cordierite / silicon carbide composite honeycomb ceramic obtained in step 1 is sequentially immersed in the three impregnation solutions prepared in step 2. The impregnation process is as follows: first, it is immersed in one impregnation solution, placed at a low temperature to promote the formation of whiskers and allow the whiskers to bond with the matrix, and then dried; then it is transferred to another impregnation solution, and the above steps are repeated in the three impregnation solutions respectively. After the third drying, the honeycomb ceramic is placed in a corundum crucible and sintered in a muffle furnace at 900~1100 ℃ for 1-3 h. After natural cooling, it is taken out.

[0020] The purpose of silica sol impregnation is to introduce silica into the surface of composite ceramics. Aluminum nitrate is used to introduce the silicon source. After high-temperature decomposition, it can generate alumina. Under high-temperature heat preservation, alumina and silica generate mullite grains. Ammonium fluoride decomposes at high temperature to generate fluoride ions, which are adsorbed on specific crystal faces of mullite grains, causing whiskers to grow in specific directions to form mullite whiskers.

[0021] In some embodiments of the present invention, the cordierite / silicon carbide composite honeycomb ceramic material prepared based on the above conditions in step 1 has a porosity ≥49.24%, a flexural strength ≥3.01 MPa, and does not crack after at least 15 thermal shock cycles at room temperature to 650 ℃; its collection efficiency is not less than 87.45%; and its acid corrosion rate is not higher than 1.42%.

[0022] In some embodiments of the present invention, the whisker-reinforced composite porous ceramic material involves in-situ generation of mullite whiskers on the surface of the cordierite / silicon carbide composite honeycomb ceramic matrix. The formation of mullite whiskers increases the specific surface area of ​​the cordierite / silicon carbide composite honeycomb ceramic matrix, thereby improving the filtration accuracy and filtration efficiency of the cordierite / silicon carbide composite honeycomb ceramic matrix porous filter material.

[0023] In some embodiments of the present invention, the preparation method of the cordierite / silicon carbide composite honeycomb ceramic material is as follows: 40 wt.% cordierite powder, 60 wt.% silicon carbide powder and 6 wt.% carbon powder are mixed; wherein the particle size of the silicon carbide powder is 300 mesh; titanium dioxide is added as a sintering aid, polyvinyl alcohol aqueous solution as a binder, as well as hydroxypropyl methylcellulose, deionized water and glycerin, and after mixing, the mixture is kneaded, aged, extruded and sintered to obtain the final product.

[0024] In step 1, the cordierite / silicon carbide composite honeycomb ceramic material prepared under optimal conditions has a porosity of 52.94%, an acid corrosion rate of 0.83%, a thermal shock cycle life of 20 cycles, a compressive strength of 7.94 MPa, a flexural strength of 20.55 MPa, a trapping efficiency of 90.15%, and a coefficient of thermal expansion of 3.65 × 10⁻⁶. -6 / ℃.

[0025] In step 2, a whisker-reinforced composite porous ceramic material is prepared from the cordierite / silicon carbide composite honeycomb ceramic material prepared under the optimal conditions in step 1. This material has a porosity of 52.91%, an acid corrosion rate of 0.83%, and withstands 18 thermal shock cycles. Its compressive strength is 8.06 MPa, its flexural strength is 25.10 MPa, and its trapping efficiency reaches 95.66%. Its coefficient of thermal expansion is 3.88 × 10⁻⁶. -6 / ℃.

[0026] Thirdly, the present invention provides the application of the whisker-reinforced composite porous ceramic material described in the first aspect in the preparation of filter materials.

[0027] Fourthly, the present invention provides the application of the whisker-reinforced composite porous ceramic material described in the first aspect in a diesel particulate filter (DPF).

[0028] DPFs, as filter media, must be porous. However, porosity is one of the most significant factors weakening the mechanical strength of materials. Pores, like internal defects, cause stress concentration, leading to failure under lower loads. Therefore, DPF design aims to achieve the highest possible compressive and flexural strength while ensuring sufficient porosity to meet filtration and low pressure drop requirements.

[0029] This invention reveals that in cordierite / silicon carbide composite ceramic materials, thermal shock resistance is affected not only by the cordierite content but also by variations in silicon carbide particle size. However, adjustments to both raw material content and silicon carbide particle size lead to fluctuations in filtration efficiency. Achieving simultaneous improvement in both properties is a key technical challenge. The inventors have been pleased to discover that the cordierite / silicon carbide composite ceramic material prepared using the optimized method of this invention possesses not only excellent thermal shock resistance but also superior mechanical properties and trapping effect. Through mullite whisker reinforcement, the product prepared in this invention exhibits significantly higher flexural strength than both the cordierite / mullite and silicon carbide / mullite groups, ensuring good flexural strength while improving trapping efficiency. Furthermore, the resulting whisker-reinforced composite porous ceramic material demonstrates excellent thermal shock resistance.

[0030] Silicon carbide itself possesses high hardness and strength, while cordierite and mullite provide excellent thermal shock resistance. When these three materials recombine, the silicon carbide particles act as a framework, while the microcrystals of cordierite and mullite fill the gaps between the silicon carbide grains, forming a denser and more resilient structure. The whisker-reinforced composite porous ceramic material provided by this invention achieves superior overall performance in multiple dimensions, including mechanical strength, thermal shock resistance, filtration efficiency, and cost.

[0031] Compared with the prior art, the technical solution provided by this invention has the following beneficial effects: 1. This invention provides a whisker-reinforced composite porous ceramic material and its preparation method. Under the cordierite and silicon carbide content ratio provided by this invention, combined with factors such as silicon carbide particle size and sintering conditions, the low thermal expansion performance of cordierite and the high mechanical strength of silicon carbide are truly achieved, resulting in a composite material with high filtration effect, thermal shock resistance, and mechanical strength. This overcomes the defect of sacrificing other properties to achieve only a single performance improvement in the prior art. It provides a filter material with excellent thermal shock resistance, high collection efficiency, and good mechanical strength that is suitable for diesel particulate filters (DPFs).

[0032] 2. This invention provides a method for preparing whisker-reinforced composite porous ceramic materials. The process is simple and suitable for industrial production. This ceramic extrusion molding process has the core advantage of being simple and easy to implement. Compared to dry pressing, it eliminates the steps of powder granulation and step-by-step pressure control. Compared to slip casting, it eliminates the need for preparing special slurries and a lengthy demolding and drying cycle. Only the clay material needs to be controlled to obtain a ceramic green body with a smooth surface and uniform internal structure. The process has low equipment dependence; ordinary laboratories or small and medium-sized production enterprises can carry out production with a basic extruder, combining economic efficiency and practicality.

[0033] 3. The product of this invention has high porosity and excellent compressive strength. The addition of carbon powder significantly improves the porosity of the ceramic. Furthermore, the use of silicon carbide as the main raw material, with its strong covalent bond characteristics and high density and low defect microstructure, significantly enhances the mechanical properties of the material.

[0034] 4. The product of this invention exhibits excellent thermal shock resistance. By adding cordierite and silicon carbide powder, the low expansion characteristics of cordierite, the high thermal conductivity and high toughness of silicon carbide, and the synergistic effect of the microstructure formed after their composite enhance the material's thermal shock resistance. The coefficient of thermal expansion of the prepared composite honeycomb ceramic is 3.65 × 10⁻⁶. -6 / ℃; The coefficient of thermal expansion of the mullite whisker-reinforced cordierite / silicon carbide composite filter material is 3.88×10. -6 / ℃.

[0035] 5. The product of this invention has excellent chemical stability. The raw materials selected in this invention, after molding, have excellent chemical inertness and the two-phase interface is tightly bonded. After the formation of whiskers, the whiskers fill the bonding area of ​​the matrix, greatly reducing the channels for acid solution to penetrate into the material and avoiding the problem of chemical corrosion, thus significantly improving the chemical stability of the material.

[0036] 6. The product of this invention has excellent capture efficiency. While maintaining high porosity, it uses mullite whiskers for reinforcement, generating slender needle-shaped mullite whiskers that interlock in the matrix to form a three-dimensional network skeleton. This significantly increases the tortuosity of the capture channels, making it easier for particles to collide with and be intercepted by the whiskers as they pass through, thus further improving the material's capture efficiency for particles. Attached Figure Description

[0037] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0038] Figure 1 SEM images of cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics are shown; where a is cordierite / silicon carbide composite ceramic and b is cordierite / silicon carbide / mullite whisker composite ceramic.

[0039] Figure 2 The diagram shows the compressive strength of cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics.

[0040] Figure 3 The diagram shows the flexural strength of cordierite / mullite whisker composite ceramics, cordierite / silicon carbide / mullite whisker composite ceramics, and silicon carbide / mullite whisker composite ceramics.

[0041] Figure 4 Porosity diagrams for cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics.

[0042] Figure 5 Pore ​​size distribution diagrams for cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics.

[0043] Figure 6 The diagram shows the corrosion resistance of cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics.

[0044] Figure 7 The thermal shock resistance diagrams are for cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics.

[0045] Figure 8 The graph shows the collection efficiency of cordierite / silicon carbide composite ceramics and cordierite / silicon carbide / mullite whisker composite ceramics. Detailed Implementation

[0046] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0047] The present invention will be further described below with reference to the embodiments.

[0048] Example 1 Preparation of cordierite / silicon carbide composite honeycomb ceramics Step 1: Preparation of raw materials and equipment Cordierite (2MgO·2Al2O3·5SiO2) powder was purchased from Jiangxi Henghao New Material Technology Co., Ltd., Jiangxi, China; silicon carbide (SiC) powder was purchased from Shandong Huaen New Material Co., Ltd., Shandong, China.

[0049] The ceramic extrusion molding equipment used was a laboratory ceramic tube extruder LWJ-63, purchased from Zhongbo Ceramic Machinery Factory.

[0050] The types and amounts of raw materials, process steps, equipment, etc., not described in the embodiments and comparative examples of this invention all use commonly used raw materials, processes and equipment in the field, and these undescribed contents are consistent in the embodiments and comparative examples.

[0051] Cordierite powder with a particle size of 300 mesh and silicon carbide powder with a particle size of 200-500 mesh (the total mass content of cordierite and silicon carbide powders is 100%), along with 10 wt.% carbon powder relative to the cordierite and silicon carbide powders, were mixed in a mixer for 0.5 h to ensure uniform distribution. Subsequently, titanium dioxide was added as a sintering aid, relative to the cordierite and silicon carbide powders at 0-9 wt.%.

[0052] A 5% polyvinyl alcohol aqueous solution (6%) was added as a binder, along with 8% HPMC, 32% deionized water, and 5% glycerol. The mixture was kneaded in a mixer for 0.5 h to form a homogeneous clay. Subsequently, it underwent three pre-homogenization treatments under non-vacuum conditions using a vacuum kneader, followed by five vacuum treatments to further remove air bubbles and impurities, ensuring density and homogeneity. The treated clay was wrapped in plastic film and aged in a sealed container for 48 h. After aging, the clay was shaped using a laboratory ceramic extruder. The shaped samples were dried at room temperature for 48 h to remove excess moisture. Finally, the dried samples were sintered using heating programs of room temperature to 400 °C at 4 °C / min; 400 to 1000 °C at 3 °C / min; and 1000 to 1150 °C at 2 °C / min, and held at the final sintering temperature for 3 h at each temperature. After the sintering process, the samples were cooled to room temperature in the furnace to obtain honeycomb cordierite / silicon carbide composite ceramics.

[0053] The performance of the products prepared in the examples was tested, including porosity, acid corrosion rate, number of thermal shock cycles, compressive strength, and flexural strength.

[0054] The porosity detection method and calculation formula are as follows: A ceramic water absorption tester is used for porosity testing. During the test, the dry weight of the sample is measured using a balance. After evacuating the water absorption tester for 10 minutes, the wet weight and buoyant weight of the sample are measured using a balance, and the porosity of the sample is calculated. Archimedes' displacement method is used to test the porosity of the sample.

[0055] Acid corrosion rate, typically measured by the degree of resistance to acid and alkali corrosion, characterizes the chemical stability of ceramic supports. The acid corrosion rate is determined by placing a fully dried support in an H₂SO₄ solution with pH=1, gently boiling it in a 90 ℃ water bath for 1 h, then allowing it to stand in the solution for 7 days. After the test, the sample is thoroughly cleaned until neutral and then dried to constant weight. The chemical stability of the ceramic support is characterized by the mass loss method.

[0056] The method for testing the number of thermal shock cycles is as follows: the temperature of the box-type resistance furnace (muffle furnace) is controlled at 650 ℃, and then the cordierite honeycomb ceramic carrier is placed in the furnace chamber. After holding at the temperature for 30 min, it is quickly taken out and naturally cooled to room temperature (about 6 ℃). This operation is considered as one thermal shock cycle. The thermal shock cycle is repeated until cracks appear on the wall of the honeycomb ceramic carrier. The number of cycles is used to characterize the thermal shock resistance of the honeycomb ceramic carrier.

[0057] The standard for compressive strength testing is JC / T 2396-2017.

[0058] The standard for testing flexural strength is GB / T 9341-2008.

[0059] The particle trapping efficiency was determined by gravimetric analysis. Specifically, 0.05 g of carbon powder was dispersed in anhydrous ethanol to form a stock solution of 2000 ppm. Before testing, each sample was dried at 110°C for 10 h, and its initial mass (M0) was recorded. The sample was then mounted in a self-made testing instrument, and the solution was injected into an atomizer to generate carbon black aerosol. The nitrogen carrier gas flow rate was set to 100 mL / min. After the test, the sample was thoroughly dried to remove the ethanol and weighed again (M1). The mass gain (ΔM1 = M1) was calculated. M0 represents the mass of the captured carbon black. Furthermore, the carbon aerosol was thoroughly dried to remove ethanol and weighed again (M3). The mass loss of the carbon powder is ΔM2 (ΔM2 = 0.05 g). M3). The formula for calculating the filtration efficiency (η) is η=(ΔM1 / ΔM2)×100%.

[0060] The preparation parameters and detection results in the examples are shown in Table 1: Table 1 Summary of Preparation Process and Product Testing Results serial number Silicon carbide content / wt.% Silicon carbide particle size / mesh Firing aid content / wt.% Porosity / % Acid corrosion rate / % Thermal shock resistance cycles Compressive strength / MPa 1 20 200 0 64.966 1.05 5 1.65 2 20 300 3 57.1023 1.15 20 2.11 3 20 400 6 56.3696 1.52 20 4.19 4 20 500 9 54.5398 1.93 13 3.68 5 40 200 3 58.3318 0.61 6 2.35 6 40 300 0 58.8316 2.53 18 4.70 7 40 400 9 55.7258 0.74 12 4.48 8 40 500 6 57.0862 1.51 14 8.44 9 60 200 6 51.3899 1.13 17 5.48 10 60 300 9 48.8525 1.84 12 5.44 11 60 400 0 52.2672 1.11 18 4.65 12 60 500 3 51.3451 2.17 18 10.21 13 80 200 9 50.5745 0.24 11 5.46 14 80 300 6 58.3991 0.24 18 4.31 15 80 400 3 57.5757 1.36 8 1.89 16 80 500 0 58.1159 1.67 18 4.08 The key performance characteristic studied in this invention is the number of thermal shock cycles, which determines the service life of the material. Therefore, the number of thermal shock cycles is used as the main basis, and K is calculated based on the range. （SiC粒径） =7.25>K （助烧剂含量） =5.25>K （SiC含量） =3.75, therefore we can conclude that silicon carbide particle size has the greatest impact on material properties.

[0061] Based on the above results, experiments were conducted with different silicon carbide particle sizes, under the conditions of silicon carbide powder content of 60 wt.%, titanium dioxide as sintering aid of 6 wt.%, and other preparation processes remaining unchanged. The results are shown in Table 2. Table 2 Summary of the Influence of Different Silicon Carbide Particle Sizes on Product Performance serial number Particle size / mesh Porosity Acid corrosion rate / % thermal shock cycles Compressive strength / MPa Capture efficiency / % 1 200 55.89 0.52 15 3.01 90.96 2 300 52.94 0.83 20 7.94 90.15 3 400 51.47 0.57 16 3.71 88.78 4 500 49.24 1.42 18 8.21 87.45 Based on the results in Tables 1 and 2, the optimal raw material ratio is determined to be 60 wt.% silicon carbide powder, 300-mesh silicon carbide powder, and 6 wt.% titanium dioxide as a sintering aid.

[0062] Example 2 Preparation of cordierite / silicon carbide / mullite whisker composite ceramics Mullite whiskers were generated using methods provided in existing literature (Ai Chaoqian, Study on Surface Modification and Catalytic Performance of Cordierite Porous Ceramics [D]. Chang'an University, 2020): Three impregnation solutions were prepared. A silica sol with a concentration of 0.99 mol / L was prepared using tetraethyl orthosilicate, anhydrous ethanol, deionized water, and ammonia. The specific method was as follows: anhydrous ethanol was measured into a beaker, and tetraethyl orthosilicate was measured into the beaker. An appropriate amount of distilled water was added, and the mixture was stirred continuously with a magnetic stirrer. 2-3 drops of ammonia were added dropwise to catalyze the hydrolysis of tetraethyl orthosilicate. The mixture was stirred overnight to prepare the silica sol.

[0063] Weigh a certain amount of aluminum nitrate nonahydrate to prepare a 1.98 mol / L aluminum nitrate solution.

[0064] Weigh out a certain amount of ammonium fluoride and prepare an ammonium fluoride solution with a concentration of 8.91 mol / L.

[0065] Preparation of mullite whiskers The cordierite / silicon carbide composite honeycomb ceramic prepared in Example 1 was sequentially immersed in three impregnation solutions prepared in this example, each for 60 min. The honeycomb ceramic, along with the impregnation solution, was then transferred to a refrigerator (temperature -6°C) and kept there for 30 min to allow the precursor to disperse evenly and promote whisker formation, thus bonding the whiskers to the matrix. The honeycomb ceramic was then removed and dried in an electric thermostatic drying oven at 55°C for 15 h, before being transferred to another impregnation solution. This process was repeated with each of the three impregnation solutions. After the third drying, the honeycomb ceramic was placed in a corundum crucible and sintered in a muffle furnace at 900-1100°C for 1-3 h. After natural cooling, it was removed.

[0066] The optimal sample of cordierite / silicon carbide composite honeycomb ceramic prepared in Example 1 was impregnated in silica sol solution, aluminum nitrate solution, and ammonium fluoride solution, respectively, and held at 1000℃ for 2 hours to obtain cordierite / silicon carbide / mullite whisker composite ceramic. Its porosity was measured to be 52.91%, acid corrosion rate to be 0.81%, compressive strength to be 8.06 MPa, flexural strength to be 25.10 MPa, and thermal shock resistance to be 18 cycles. The coefficient of thermal expansion was 3.65 × 10⁻⁶. -6 / ℃.

[0067] Example 3 Preparation of cordierite / mullite whisker composite ceramics Replacing the silicon carbide and cordierite powder in Example 1 with 300-mesh pure cordierite powder and following the experimental procedures of Examples 1 and 2, the prepared material had a porosity of 67.3%, a compressive strength of 5.71 MPa, a flexural strength of 16.90 MPa, and could withstand 7 thermal shock cycles. Its coefficient of thermal expansion was 3.88 × 10⁻⁶. -6 / ℃.

[0068] Example 4 Preparation of silicon carbide / mullite whisker composite ceramics The silicon carbide and cordierite powder in Example 1 were replaced with 300-mesh pure silicon carbide powder, and the experimental steps of Example 1 and Example 2 were repeated. The prepared material had a porosity of 58.38%, a compressive strength of 8.38 MPa, a flexural strength of 20.95 MPa, and could withstand 5 thermal shock cycles.

[0069] A comparison with Example 2 shows that the thermal shock resistance and mechanical properties of Examples 3 and 4 are far inferior to those of Example 2, and cannot meet the requirements for long-term use of the product in high-temperature environments.

[0070] Test case The range calculated in Table 1 reveals that the silicon carbide particle size has the greatest overall impact. Comparison of different particle sizes shows that a particle size of 300 mesh exhibits the best overall performance, with a porosity of 52.94%, a thermal shock resistance of 20 cycles, a compressive strength of 7.94 MPa, and a particle trapping efficiency of 90.15%. Therefore, 300 mesh was selected as the matrix for whisker formation. The prepared cordierite / silicon carbide / mullite whisker composite ceramic material was characterized.

[0071] from Figure 1 Image a is a 50-micrometer scan image of cordierite / silicon carbide composite ceramic, showing a three-dimensional interconnected structure in the porous material. Figure 1 Image b shows a scanned image of cordierite and silicon carbide ceramics after whisker formation. It reveals the formation of elongated, needle-like mullite whiskers that interlock within the matrix to form a three-dimensional network framework. This significantly increases the tortuosity of the trapping channels, making it easier for particles to collide with and be intercepted by the whiskers, thus further improving the material's particle trapping efficiency. Furthermore, the formation of whiskers increases the specific surface area of ​​the material, enhancing its adsorption of fine particles and further improving the trapping efficiency (95.66%). Figure 8 It can be seen that the collection efficiency changes significantly before and after whisker formation.

[0072] With the formation of whiskers, the compressive strength of composite materials is significantly improved due to their bridging, pull-out, and crack deflection effects, as well as their ability to fill matrix pores and reduce stress concentration points. However, whisker formation also introduces additional defects. Uneven whisker dispersion in the matrix can lead to cracking under stress, further reducing the material's strength. These two factors cancel each other out, ultimately resulting in a decrease in the compressive strength of the composite material after whisker reinforcement. Figure 2 The result shows a slight enhancement.

[0073] like Figure 3 As shown, the flexural strength improved after the formation of mullite whiskers. The main reason for this improvement is that the whiskers fill the pores in the matrix, reducing internal defects and increasing density, thus reducing the risk of fracture caused by defects. Furthermore, when a crack propagates in the matrix and encounters mullite whiskers, it is forced to change its propagation direction. This process lengthens the crack path, consumes more energy, and prevents fracture caused by rapid crack penetration. The whiskers can span across the crack, acting as a "bridge" to bear and transfer stress. They can delay crack opening, continuously absorb fracture energy, and thus improve the overall deformation resistance of the material.

[0074] like Figure 4 As shown, after whiskers are generated, micropores are left in situ, and the whiskers form a spatial network structure, which hinders the rearrangement and densification of particles during sintering, resulting in increased porosity. However, during the whisker generation process, as the liquid phase sinters, the liquid phase also fills the original micropores of the matrix, thereby reducing the porosity. The combination of these two factors also results in no significant change in porosity.

[0075] like Figure 5 As shown in the pore size distribution curve, the introduction of mullite whiskers significantly alters the pore size characteristics of cordierite / silicon carbide ceramics. After the formation of mullite whiskers, the proportion of low-pore size increases significantly. This is because the introduction of whiskers fills the gaps between cordierite and mullite particles, thereby refining the pore size and increasing the proportion of low-pore size, which leads to an improvement in the trapping efficiency and provides more active sites for fine particles.

[0076] like Figure 6 As shown, the introduction of mullite whiskers reduces the acid corrosion rate of the composite material, combined with... Figure 1 Scanning analysis revealed that the whiskers are evenly distributed and have a continuous structure, which fills the pores inside the matrix and hinders the penetration of acid into the material, reducing the contact area between the material and the acid, thereby enhancing the corrosion resistance of the material.

[0077] like Figure 7As shown, during the whisker formation process, the temperature difference between the inside and outside of the material increases sharply due to the drying and freezing after impregnation, resulting in instantaneous thermal stress. Furthermore, the subsequent heat preservation and cooling of the material at 1000 ℃ will also generate thermal stress at the material interface, gradually initiating microcracks and continuously expanding, which leads to a decrease in the number of thermal shock cycles.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A whisker-reinforced composite porous ceramic material, characterized in that, The invention comprises cordierite / silicon carbide composite honeycomb ceramic as the matrix and mullite whiskers in the matrix; the cordierite / silicon carbide composite honeycomb ceramic uses cordierite powder and silicon carbide powder as the main raw materials, hydroxypropyl methylcellulose as the plasticizer, carbon powder as the pore-forming agent, titanium dioxide as the sintering aid, glycerin as the lubricant, polyvinyl alcohol solution and deionized water are added and mixed evenly, vacuum-refined and aged, extruded with a honeycomb mold, dried, and obtained by reaction sintering.

2. A method for preparing a whisker-reinforced composite porous ceramic material, characterized in that, First, a composite porous honeycomb ceramic material was obtained by reaction sintering using cordierite powder and silicon carbide powder as the main raw materials. Then, the surface of the composite porous honeycomb ceramic material was enhanced by impregnation in an impregnation solution to provide the Si and Al sources required for the synthesis of mullite whiskers.

3. The method for preparing the whisker-reinforced composite porous ceramic material according to claim 2, characterized in that, Includes the following steps: Step 1: Preparation of cordierite / silicon carbide composite honeycomb ceramics Mix 20-80 wt.% cordierite powder, 20-80 wt.% silicon carbide powder, and 0-15 wt.% carbon powder; wherein the particle size of the silicon carbide powder is 200-500 mesh; add titanium dioxide as a sintering aid, polyvinyl alcohol aqueous solution as a binder, as well as hydroxypropyl methylcellulose, deionized water, and glycerin, mix, knead into a paste, age, extrude into shape, and sinter to obtain the final product; Step 2: Mullite whiskers are generated in situ from the cordierite / silicon carbide composite honeycomb ceramic prepared in Step 1.

4. The method for preparing the whisker-reinforced composite porous ceramic material according to claim 3, characterized in that, In step 1, 0-9 wt.% titanium dioxide, 0.27-0.33 wt.% polyvinyl alcohol, 7-9 wt.% hydroxypropyl methylcellulose, 29-35 wt.% deionized water and 4.5-5.5 wt.% glycerol are added relative to the content of cordierite and silicon carbide powder.

5. The method for preparing the whisker-reinforced composite porous ceramic material according to claim 3, characterized in that, Step 1 includes the following steps: Step 101: Mix the materials according to the required proportions; Step 102: The mixed raw materials are subjected to ordinary mud refining and vacuum mud refining; Step 103: Seal and age the mud block obtained in step 102 for 44-52 hours; Step 104: Use a ceramic extrusion molding equipment to extrude the clay block obtained in step 103 into a mold and then age it for 44-52 hours. Step 105: Sinter and hold for 2-4 hours with a heating program of room temperature ~ 400 ℃: 4 ℃ / min; 400~1000 ℃: 3 ℃ / min; 1000~1150 ℃: 2 ℃ / min.

6. The method for preparing the whisker-reinforced composite porous ceramic material according to claim 3, characterized in that, In step 2, silica sol, aluminum nitrate solution, and ammonium fluoride solution are prepared respectively. The cordierite / silicon carbide composite honeycomb ceramic obtained in step 1 is sequentially immersed in the three impregnation solutions prepared in step 2. The impregnation process is as follows: first, it is immersed in one impregnation solution, placed at a low temperature to promote the formation of whiskers and allow the whiskers to bond with the matrix, and then dried; then it is transferred to another impregnation solution, and the above steps are repeated in the three impregnation solutions respectively. After the third drying, the honeycomb ceramic is placed in a corundum crucible and sintered in a muffle furnace at 900-1100 ℃ for 1-3 h. After natural cooling, it is taken out.

7. The method for preparing the whisker-reinforced composite porous ceramic material according to claim 3, characterized in that, The cordierite / silicon carbide composite honeycomb ceramic material prepared in step 1 has a porosity ≥49.24%, a flexural strength ≥3.01 MPa, and does not crack after at least 15 thermal shock cycles at room temperature to 650 ℃; its collection efficiency is not less than 87.45%; and its acid corrosion rate is not higher than 1.42%.

8. The method for preparing the whisker-reinforced composite porous ceramic material according to claim 3, characterized in that, The preparation method of the cordierite / silicon carbide composite honeycomb ceramic material is as follows: 40 wt.% cordierite powder, 60 wt.% silicon carbide powder and 6 wt.% carbon powder are mixed; wherein the particle size of silicon carbide powder is 300 mesh; titanium dioxide is added as a sintering aid, polyvinyl alcohol aqueous solution as a binder, as well as hydroxypropyl methylcellulose, deionized water and glycerin, and after mixing, the mixture is kneaded, aged, extruded and sintered to obtain the final product.

9. The application of the whisker-reinforced composite porous ceramic material according to claim 1 in the preparation of filter materials.

10. The application of the whisker-reinforced composite porous ceramic material as described in claim 1 in a diesel engine particulate filter.

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