A skin graft material, applications and a method for preparing silicon carbide honeycomb ceramics

Abstract

The application relates to the technical field of honeycomb ceramics, in particular to a skin grafting material, application and preparation method of silicon carbide honeycomb ceramics. The skin grafting material comprises main materials and auxiliary materials, the main materials comprise silicon carbide powder, metal silicon powder and ceramic fibers, the auxiliary materials comprise a plasticizer, a water reducing agent and a mixed solvent, the mixed solvent comprises ethanol and / or isopropyl alcohol, and the mass of the alcohol is 8-15% of the main materials. The skin grafting material utilizes the rapid volatilization of alcohol at a low temperature section to take away a large amount of heat and water, significantly shortens the drying time and realizes energy saving and consumption reduction; the method adopts three-section gradient drying, so that water and alcohol are orderly removed in stages, and the drying process is ensured not to crack. The silicon carbide honeycomb ceramics remain not to crack and not to fall off under high-temperature thermal shock cycles, and have good acid corrosion resistance.

Description

Technical Field

[0001] This invention relates to the field of honeycomb ceramic technology, and more specifically, to a seed coat, its application, and a method for preparing silicon carbide honeycomb ceramics. Background Technology

[0002] SiC materials possess characteristics such as high high-temperature strength, good oxidation resistance, wear resistance, good thermal stability, low coefficient of thermal expansion, high thermal conductivity, and high hardness. Due to their excellent performance, silicon carbide honeycomb ceramics prepared from SiC are mainly used in off-road equipment in harsh and complex environments, primarily serving to filter particulate matter (PM). They are also known as wall-flow filters. In wall-flow filters, there are continuously distributed micropores on the rib walls. When the PM particle size is larger than the micropore size, these PM particles will block the micropores and accumulate on the surface of the rib walls, affecting the filtration efficiency.

[0003] There are two solutions to eliminate PM blockages. One is to decompose and remove PM through combustion or other means. However, this method has limited removal efficiency and also has problems such as requiring additional energy consumption, generating secondary pollution, and increasing fuel consumption.

[0004] Another approach is to coat the wall-flow carrier with expensive metal catalysts and use these catalysts to decompose PM. This method can effectively remove PM without causing secondary pollution or other problems.

[0005] Since most silicon carbide cell ceramic filters (DPFs) are currently circular or elliptical in shape, and these circular and elliptical structures are obtained by machining multiple silicon carbide square units, the finished products lack outer skin protection, resulting in a significant reduction in their service life.

[0006] Traditional peripheral skin grafts suffer from slow drying, cracking, poor protective effect, and high cost. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a grafting material, its application, and a method for preparing silicon carbide honeycomb ceramics.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: Based on the above technical solution, the present invention can be further improved as follows.

[0009] The grafting material of the present invention includes a main material and auxiliary materials. The main material includes silicon carbide powder, metallic silicon powder and ceramic fiber. The auxiliary materials include plasticizer, water reducing agent and mixed solvent. The mixed solvent includes ethanol and / or isopropanol, and the mass of the alcohol is 8-15% of the main material.

[0010] Furthermore, the mixed solvent also includes water, the mass of which is 1%-10% of the main ingredient.

[0011] Furthermore, the auxiliary materials also include a powder binder and a liquid binder; the mass of the powder binder is 0.5%-1.5% of the main material, the mass of the liquid binder is 30%-40% of the main material, the mass of the plasticizer is 0.1%-0.5% of the main material, and the mass of the water-reducing agent is 0.1%-0.5% of the main material.

[0012] Furthermore, the powder binder is at least one of methylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose; the liquid binder is at least one of silica sol, aluminum sol, and silica-alumina sol; the plasticizer is at least one of PEG-400, PEO, and PVA; and the water-reducing agent is at least one of PAA-NH4, PMAA-NH4, and PCE.

[0013] Furthermore, in the main material, the silicon carbide powder accounts for 85-95%, the metallic silicon powder accounts for 0.1-5%, and the ceramic fiber accounts for 5-9.9%.

[0014] Furthermore, the main material, the silicon carbide powder, includes, in descending order of mass percentage, 80-100μm silicon carbide particles, 60-70μm silicon carbide particles, 30-40μm silicon carbide particles, and silicon carbide particles smaller than 3μm. The particle size of the metallic silicon is 4-10 μm; The ceramic fiber has a length of 40-200μm and a diameter of 5-20μm, and the material of the ceramic fiber is at least one of alumina, calcium silicate, silicon nitride, mullite, and silicon carbide fiber.

[0015] The present invention also provides the application of the above-described grafting material in the preparation of silicon carbide honeycomb ceramics.

[0016] The present invention also provides a silicon carbide honeycomb ceramic, wherein the surface of the silicon carbide honeycomb ceramic is provided with the skin material as described above.

[0017] The present invention also provides a method for preparing silicon carbide honeycomb ceramic as described above, wherein the skin material is coated on the outer surface of the silicon carbide honeycomb ceramic substrate, and then the silicon carbide honeycomb ceramic carrier is obtained by a three-stage gradient heating and drying method.

[0018] Furthermore, in the three-stage gradient heating drying process, the temperature of the first stage of drying is 40-60℃ and the drying time is 0.5-1h; the temperature of the second stage of drying is 80-120℃ and the drying time is 0.5-1h; and the temperature of the third stage of drying is 150-200℃ and the drying time is 1-1.5h; the heating rate between each stage of drying is 3-6℃ / min.

[0019] The beneficial effects of this invention are as follows: (1) The grafting material of the present invention uses a mixed solvent, which utilizes the rapid evaporation of alcohol at low temperature to remove a large amount of heat and moisture, significantly shortening the drying time and achieving energy saving and consumption reduction; (2) The grafting material of the present invention introduces a water-reducing agent to effectively reduce the amount of liquid added, avoid excessive moisture leading to excessive drying shrinkage and cracking, and ensure the integrity of the grafting layer structure; the addition of a plasticizer not only improves the problem of insufficient plasticity caused by the increase in solid content, but also acts as a pore-forming agent to form a microporous structure, buffering the thermal stress during rapid cooling and heating, and significantly improving thermal shock stability. (3) The grafting material of the present invention uses silicon carbide powder and ceramic fiber with multi-level particle size, which can form a strong chemical bond without high-temperature sintering, greatly reducing production energy consumption and cost; (4) The silicon carbide honeycomb ceramic preparation method of the present invention adopts a three-stage gradient drying method to remove moisture and alcohol in stages and in an orderly manner, avoid vapor pressure accumulation and local overheating, and ensure that the drying process does not crack. (5) The silicon carbide honeycomb ceramic of the present invention has a skin material of the present invention on its surface. It does not crack or fall off under high temperature thermal shock cycle and has good acid corrosion resistance. This shows that its matrix can be effectively protected by the skin material. At the same time, the production cost is low, the preparation energy consumption is low, and the service life and use effect are effectively improved. Attached Figure Description

[0020] Figure 1 This is a SEM image of the grafting material in Example 1 of the present invention. Detailed Implementation

[0021] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0022] The grafting material of the present invention includes a main material and auxiliary materials. The main material includes silicon carbide powder, metallic silicon powder and ceramic fiber. The auxiliary materials include plasticizer, water reducing agent and mixed solvent. The mixed solvent includes ethanol and / or isopropanol, and the mass of the alcohol is 8-15% of the main material.

[0023] The grafting material of this invention uses a mixed solvent in its excipients. The alcohol rapidly removes a large amount of heat and moisture through evaporation at lower temperatures, significantly improving the initial drying rate. Simultaneously, the initial evaporation of the alcohol opens up some moisture migration channels, facilitating smoother water evaporation at medium temperatures. The plasticizer acts as both plasticizer and pore-forming agent, effectively reducing internal stress and improving plasticity. The water-reducing agent reduces the amount of liquid added, preventing excessive liquid from causing product cracking. This grafting material can be applied to the surface of silicon carbide honeycomb ceramic DPF, providing good protection even for silicon carbide honeycomb ceramic DPFs with circular or elliptical structures.

[0024] Preferably, the mixed solvent also includes water, with the water content being 1%-10% of the main material.

[0025] Preferably, the alcohol is ethanol and the water is purified water.

[0026] Preferably, the mass of ethanol is 10% of the main raw material, and the mass of water is 3% of the main raw material.

[0027] The grafting material of the present invention further includes a powder binder and a liquid binder in its auxiliary materials; the powder binder can provide the grafting material with plasticity, formability and water retention capacity at room temperature, ensuring that the coating is easy to apply and not easy to crack; the liquid binder forms a three-dimensional network through the condensation reaction of the hydroxyl groups on its surface, giving the grafting layer the final high-temperature strength and structural stability; through the interaction of the above auxiliary materials, the grafting material can be dried quickly during the preparation process without the need for high-temperature sintering.

[0028] Preferably, the mass of the powder binder is 0.5%-1.5% of the main material, the mass of the liquid binder is 30%-40% of the main material, the mass of the plasticizer is 0.1%-0.5% of the main material, and the mass of the water-reducing agent is 0.1%-0.5% of the main material.

[0029] Preferably, the powder binder is at least one of methylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose; the liquid binder is at least one of silica sol, aluminum sol, and silica-alumina sol; the plasticizer is at least one of PEG-400, PEO, and PVA; and the water-reducing agent is at least one of PAA-NH4, PMAA-NH4, and PCE.

[0030] Preferably, the powder binder is hydroxypropyl methylcellulose, which accounts for 0.8% of the main material by weight; the liquid binder is silica sol, which accounts for 35% of the main material by weight; the plasticizer is PEG-400, which accounts for 0.3% of the main material by weight; and the water-reducing agent is PAA-NH4, which accounts for 0.2% of the main material by weight.

[0031] The grafting material of the present invention comprises 85-95% silicon carbide powder, 0.1-5% metallic silicon powder, and 5-9.9% ceramic fiber in its main component. The use of high content of silicon carbide powder and metallic silicon powder can ensure that the grafting material matches the composition of the silicon carbide honeycomb ceramic matrix and has the same coefficient of thermal expansion, thereby preventing thermal stress cracking. The appropriate amount of ceramic fiber forms a network structure to enhance toughness and buffer thermal shock stress.

[0032] Preferably, the silicon carbide powder comprises, in descending order of mass percentage, 80-100μm silicon carbide particles, 60-70μm silicon carbide particles, 30-40μm silicon carbide particles, and silicon carbide particles smaller than 3μm. This multi-level particle size distribution silicon carbide powder system allows coarse particles to form a stable framework providing structural support, while medium-fine and ultrafine particles progressively fill the gaps to achieve the tightest packing, significantly improving density and bonding strength. This overall reduces drying shrinkage and cracking risk, ensuring the graft layer possesses excellent mechanical properties and thermal shock stability.

[0033] Preferably, the mass percentage of 80-100μm silicon carbide particles is 59.5%-71.25% of the main material, the mass percentage of 60-70μm silicon carbide particles is 8.5%-19% of the main material, the mass percentage of 30-40μm silicon carbide particles is 4.25%-8.5% of the main material, and the mass percentage of silicon carbide particles smaller than 3μm is 4.25%-8.5% of the main material.

[0034] Preferably, the particle size of the metallic silicon is 4-10 μm; Preferably, the ceramic fiber has a length of 40-200μm and a diameter of 5-20μm, and the ceramic fiber is made of at least one of alumina, calcium silicate, silicon nitride, mullite, and silicon carbide fiber.

[0035] In one embodiment of the present invention, the specific formulation of the main material is as follows: 63% 80-100μm silicon carbide, 16.2% 60-70μm silicon carbide, 6.3% 30-40μm silicon carbide, 4.5% silicon carbide with a particle size of less than 3μm, 3% metallic silicon, and 7% mullite fiber, wherein the length of the mullite fiber is 50-150μm and the diameter is 10-15μm.

[0036] The grafting material of this invention can be used to prepare silicon carbide honeycomb ceramics; the silicon carbide honeycomb ceramics can be various commercially available silicon carbide honeycomb ceramics. This grafting material achieves rapid drying and sintering-free processing through the synergistic effect of an alcohol-water composite solvent, a water-reducing agent, and a plasticizer, significantly reducing energy consumption and production cycle. Furthermore, its thermal expansion coefficient matches that of the silicon carbide honeycomb ceramic matrix, effectively preventing thermal stress cracking, significantly improving thermal shock stability and structural strength, and providing reliable external protection for silicon carbide honeycomb ceramic products.

[0037] The silicon carbide honeycomb ceramic of the present invention has a skin material on its surface as described above. After the skin is applied, the silicon carbide honeycomb ceramic obtains a protective layer that is rapidly cured and does not require sintering, which significantly improves the strength of the outer structure and thermal shock stability. It does not crack or fall off under rapid cooling and heating cycles, and has excellent acid corrosion resistance. At the same time, it greatly shortens the production cycle and reduces energy consumption, ensuring that the silicon carbide honeycomb ceramic can reliably filter PM particles for a long time.

[0038] The method for preparing silicon carbide honeycomb ceramics of the present invention involves coating a skin material onto the outer surface of a silicon carbide honeycomb ceramic substrate, followed by drying using a three-stage gradient heating process to obtain a silicon carbide honeycomb ceramic carrier.

[0039] The preparation method of the present invention includes the following specific steps: 1) Add silicon carbide powder of different particle sizes, metallic silicon and powder binder into a mixer and mix to obtain mixed powder a.

[0040] Preferably, the mixing time is 50-80 minutes.

[0041] 2) First, mix the weighed water and alcohol evenly to obtain a mixed solvent. Then, add the water-reducing agent to dissolve it in the mixed solvent. Add the dissolved liquid and liquid binder to the mixing tank and disperse and stir using a disperser to obtain mixture b.

[0042] Preferably, the dispersion stirring speed is 150-250 rpm, and the time is 0.5-1.5 min. 3) Add the weighed plasticizer to mixture b and continue to disperse and stir to obtain mixture c.

[0043] Preferably, the dispersion stirring speed is 450-500 rpm and the time is 6-10 min; 4) Add the weighed ceramic fibers to mixture c and continue to disperse and stir to obtain mixture d.

[0044] Preferably, the dispersing and stirring speed is 510-550 rpm, and the time is 3-6 minutes. 5) Add the mixed powder a obtained in step 1) to the mixed material d and continue to disperse and stir to obtain the skin grafting material.

[0045] Preferably, the dispersion and stirring in this step is divided into three stages, with rotation speeds of 520 rpm, 740 rpm and 950 rpm respectively, and time periods of 4 min, 6 min and 15 min respectively.

[0046] 6) Coat the outer skin surface of the machined silicon carbide honeycomb ceramic substrate with the skin material, and then put it into the drying chamber for three-stage gradient temperature drying.

[0047] Preferably, in the three-stage gradient heating drying process, the temperature of the first stage of drying is 40-60℃ and the drying time is 0.5-1h, the temperature of the second stage of drying is 80-120℃ and the drying time is 0.5-1h, and the temperature of the third stage of drying is 150-200℃ and the drying time is 1-1.5h; the heating rate between each stage of drying is 3-6℃ / min.

[0048] In one embodiment, the temperature of the first drying stage is 50°C and the drying time is 1 hour; the temperature of the second drying stage is 110°C and the drying time is 1 hour; and the temperature of the third drying stage is 180°C and the drying time is 1.5 hours; the heating rate between each drying stage is 6°C / min.

[0049] The above three-stage gradient drying process achieves efficient drying by rapidly evaporating alcohols at low temperature to remove moisture, allowing water vapor to escape smoothly at medium temperature to avoid vapor pressure buildup, and completing structural curing and stress release at high temperature. A strong protective layer can be formed without sintering throughout the process, which significantly shortens the production cycle and reduces energy consumption. At the same time, it ensures that the skin layer is tightly bonded to the substrate and that thermal expansion is matched, giving the product excellent thermal shock stability and mechanical strength.

[0050] The effects of the present invention will be illustrated below through specific embodiments and comparative examples.

[0051] The grafting material was prepared according to the formulations of the various embodiments and comparative examples provided in Table 1, and then coated onto the surface of the silicon carbide honeycomb ceramic DPF. The main components and mass percentages of the silicon carbide honeycomb ceramic DPFs in the various embodiments and comparative examples are: SiC 63-77%, Si 16-24%, SiO 25-15%.

[0052] Then, the drying weight loss rate was calculated, thermal shock stability was tested, and acid soaking strength was tested. The SEM image of the grafting material in Example 1 is shown below. Figure 1 As shown.

[0053] The three-stage gradient heating and drying method in all embodiments and Comparative Examples 1-4 is exactly the same. The temperature of the first stage of drying is 50°C and the drying time is 1 hour; the temperature of the second stage of drying is 110°C and the drying time is 1 hour; and the temperature of the third stage of drying is 180°C and the drying time is 1.5 hours. The heating rate between each stage of drying is 6°C / min. Comparative Example 4 uses the following drying regime: the temperature is raised from room temperature to 180°C at a rate of 6°C / min, and then held at 180°C for 1.5 hours.

[0054] The specific details of each test are as follows: 1) The calculation method for drying weight loss rate is shown in the following formula: Drying weight loss rate = (Product weight after skin grafting - Product weight after drying) / Product weight after skin grafting 2) The specific method for thermal shock stability testing is as follows: Place the dried silicon carbide honeycomb ceramic structure into a muffle furnace that has reached the set temperature, hold for 30 minutes, then remove it and observe whether the outer skin cracks or makes abnormal noises. If no cracks appear, cool the product to room temperature and then place it back into the muffle furnace, repeating the above process twice. If all three thermal shock tests are satisfactory, raise the temperature by 50°C and repeat the above process again until the product cracks. The initial thermal shock temperature is set at 400°C. 3) The specific method for the acid soaking strength test is as follows: put the dried silicon carbide honeycomb ceramic structure into acid with pH=1 and soak for 30 minutes. Then put it into a muffle furnace at 450℃ and keep it at that temperature for 30 minutes. Then take it out and observe whether the skin material has fallen off. If it has not fallen off, it is qualified.

[0055] The test results are shown in Table 2.

[0056] Table 1. Skin grafting material formulations for each embodiment and comparative example. Table 2 Test results for each embodiment and comparative example The test results above show that the ethanol content in Examples 1-6 ensures good drying weight loss, no cracking, strong thermal shock stability, and good acid resistance. Comparative Example 1 cracked due to excessively low ethanol content (5%). While Comparative Example 2 significantly increased the ethanol content to 18%, achieving a drying weight loss of 39.10%, excessive volatilization caused structural instability and cracking, proving that the ethanol content needs to be moderate. Since ethanol and isopropanol have similar properties, the test results of the above examples also suggest that using isopropanol instead of ethanol or a mixture of isopropanol and ethanol can achieve similar results. When mixing isopropanol and ethanol, the ratio between the two does not need to be specifically limited.

[0057] Example 1, using a preferred ratio (10% ethanol + 3% water) with 0.3% PEG-400 and 0.2% PAA-NH4, achieved a weight reduction of 36.72% without cracking, thermal shock stability of 550℃, and qualified acid foaming strength, demonstrating the best overall performance. Examples 2 and 3, with plasticizers adjusted to 0.1% and 0.5% respectively, also maintained the absence of cracking, achieving thermal shock resistance of 450℃ and 550℃ respectively, indicating that the plasticizer concentration is adjustable within the range of 0.1-0.5%, with the upper limit showing better results.

[0058] In Example 4, reducing the water-reducing agent to 0.1% and in Example 2 to 0.2% were both successful. However, in Comparative Example 3, increasing the water-reducing agent to 0.7% led to cracking, confirming that excessive water-reducing agent can disrupt the system balance.

[0059] Comparative Example 4 used the grafting material from Example 2. After a rapid drying process, the grafting material cracked, demonstrating the necessity of using a suitable gradient temperature drying method.

[0060] It is evident that only by precisely matching the three elements of alcohol-water synergy, plasticizing and toughening, and water reduction control can sintering be avoided, rapid drying be achieved, and the skin layer be firmly bonded to the silicon carbide honeycomb ceramic matrix under high temperature and acidic conditions.

[0061] Based on the test results of the above embodiments and comparative examples, it can be demonstrated that in the existing skin grafting material system, by introducing a mixed solvent, adding plasticizers and water-reducing agents, and adopting a suitable gradient heating drying method, a silicon carbide honeycomb ceramic carrier that dries quickly and meets the performance requirements can be obtained.

[0062] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A type of plant bark material, characterized in that, It includes main materials and auxiliary materials. The main materials include silicon carbide powder, metallic silicon powder and ceramic fiber. The auxiliary materials include plasticizer, water reducing agent and mixed solvent. The mixed solvent includes ethanol and / or isopropanol, and the mass of the alcohol is 8-15% of the main materials.

2. The plant material according to claim 1, characterized in that, The mixed solvent also includes water, the mass of which is 1%-10% of the main ingredient.

3. The plant material according to claim 1, characterized in that, The auxiliary materials also include powder binder and liquid binder; the mass of the powder binder is 0.5%-1.5% of the main material, the mass of the liquid binder is 30%-40% of the main material, the mass of the plasticizer is 0.1%-0.5% of the main material, and the mass of the water-reducing agent is 0.1%-0.5% of the main material.

4. The plant material according to claim 3, characterized in that, The powder binder is at least one of methylcellulose, hydroxypropyl methylcellulose, carboxymethylcellulose, and hydroxyethylcellulose; the liquid binder is at least one of silica sol, aluminum sol, and silica-alumina sol; the plasticizer is at least one of PEG-400, PEO, and PVA; and the water-reducing agent is at least one of PAA-NH4, PMAA-NH4, and PCE.

5. A plant material according to any one of claims 1-4, characterized in that, In the main ingredients, the silicon carbide powder has a mass fraction of 85-95 parts, the metallic silicon powder has a mass fraction of 0.1-5 parts, and the ceramic fiber has a mass fraction of 5-10 parts.

6. The plant material according to claim 5, characterized in that, The main material, the silicon carbide powder, includes, in descending order of mass percentage, 80-100μm silicon carbide particles, 60-70μm silicon carbide particles, 30-40μm silicon carbide particles and silicon carbide particles smaller than 3μm. The particle size of the metallic silicon is 4-10 μm; The ceramic fiber has a length of 40-200μm and a diameter of 5-20μm, and the material of the ceramic fiber is at least one of alumina, calcium silicate, silicon nitride, mullite, and silicon carbide fiber.

7. The application of the grafting material as described in any one of claims 1-6 in the preparation of silicon carbide honeycomb ceramics.

8. A silicon carbide honeycomb ceramic, characterized in that, The surface of the silicon carbide honeycomb ceramic is provided with the skin material as described in any one of claims 1-6.

9. A method for preparing silicon carbide honeycomb ceramic as described in claim 8, characterized in that, The grafting material is coated onto the outer surface of the silicon carbide honeycomb ceramic substrate, and then dried using a three-stage gradient heating method to obtain the silicon carbide honeycomb ceramic carrier.

10. The method for preparing silicon carbide honeycomb ceramic according to claim 9, characterized in that, In the three-stage gradient heating drying process, the temperature of the first stage is 40-60℃ and the drying time is 0.5-1h; the temperature of the second stage is 80-120℃ and the drying time is 0.5-1h; and the temperature of the third stage is 150-200℃ and the drying time is 1-1.5h. The heating rate between each stage is 3-6℃ / min.

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