Mullite fiber porous ceramic as well as preparation method and application thereof

Abstract

The invention discloses mullite fiber porous ceramic as well as a preparation method and application thereof, and belongs to the technical field of ceramic fiber filters. The preparation method comprises the following steps: uniformly mixing an aluminum source compound and silica powder to obtain mixed powder; the aluminum source compound is a mixture of rho-Al2O3 and any one of gamma-Al2O3 and Al (OH) 3; wherein the amount of substance of aluminum in rho-Al2O3 accounts for 25%-75% of the amount of substance of aluminum in the aluminum source compound; uniformly mixing a hydroxypropyl methyl cellulose aqueous solution, the mixed powder and mullite fibers to obtain slurry; carrying out molding treatment on the slurry by adopting a gel-casting method to obtain a sample; the method comprises the following steps: carrying out heat preservation treatment on a sample in an air atmosphere at a first temperature to grow crystal grains, and heating to a second temperature to promote the development of a mullite crystal phase to obtain the mullite porous ceramic. The mullite fiber porous ceramic has excellent filtering efficiency.

Description

Technical Field

[0001] This invention relates to the field of ceramic fiber filter technology, and more specifically to a mullite fiber porous ceramic, its preparation method, and its application. Background Technology

[0002] With the acceleration of industrialization, air pollution has become increasingly serious, especially the flue gas emitted from energy, metallurgy, and chemical industries, which contains a large number of harmful substances such as particulate matter, sulfur oxides, and nitrogen oxides. Among these, submicron particles, with a size of less than 1 μm, can remain in the air for a longer period of time and are difficult to remove from the air through deposition, posing a serious threat to the environment and human health. Therefore, the development of efficient and durable flue gas filtration materials has become an important issue in the field of environmental protection.

[0003] Porous ceramic materials are widely used in high-temperature flue gas filtration due to their high porosity, good mechanical strength, high temperature resistance, and chemical corrosion resistance. However, traditional porous ceramic filters have long suffered from low porosity, high resistance when filtering submicron PM, and heavy weight, resulting in short service life in industrial processes. In recent years, fiber ceramic filters have attracted widespread attention from researchers due to their advantages such as high porosity, good mechanical strength, good flexibility, light weight, low filtration resistance, and high operating temperature. However, fiber ceramic filters produced by current industrial manufacturing processes suffer from high pressure drop, heavy weight, and an inability to achieve an effective balance between porosity and mechanical properties, and their filtration efficiency for submicron particles in the air remains low. Therefore, there is an urgent need to develop a new manufacturing process for fiber ceramic filters to improve their filtration efficiency for submicron particles <1μm. Summary of the Invention

[0004] To address the above problems, this invention provides a mullite fiber porous ceramic, its preparation method, and its application. The mullite fiber porous ceramic prepared by this invention has excellent filtration efficiency, solving the problems of high pressure drop, heavy weight, ineffective balance between porosity and mechanical properties, and low filtration efficiency for submicron particles in the air caused by the fiber ceramic filters prepared by current industrial production processes.

[0005] The first objective of this invention is to provide a method for preparing mullite fiber porous ceramics, comprising the following steps: uniformly mixing an aluminum source compound and silica powder to obtain a mixed powder; the aluminum source compound is any one of γ-Al2O3 and Al(OH)3 mixed with p-Al2O3; wherein the amount of aluminum in p-Al2O3 accounts for 25% to 75% of the amount of aluminum in the aluminum source compound; uniformly mixing an aqueous solution of hydroxypropyl methylcellulose, the mixed powder, and mullite fibers to obtain a slurry; and molding the slurry using a gel casting method to obtain a sample.

[0006] The dried sample was first kept at a first temperature in an air atmosphere to allow the grains to grow, and then the temperature was raised to a second temperature to promote the development of the mullite crystal phase, thus obtaining mullite porous ceramics.

[0007] During the mixing process, this invention utilizes ball milling to ensure more thorough mixing of the aluminum source compound and silicon micropowder, improving uniformity. This avoids the problem of uneven dispersion in hydroxypropyl methylcellulose aqueous solution. Traditional processes often employ vacuum filtration and pressure filtration for molding, but both are externally driven filtration molding methods. During slurry drainage, the binder in the slurry migrates directionally with the water flow, creating a concentration gradient and resulting in uneven distribution. This invention, however, employs a gel casting method. The slurry is liquid before the gel point, and after the gel point, a cross-linking reaction occurs instantaneously within the slurry, eliminating the directional flow of the binder. This solves the problem of uneven binder distribution in the vacuum filtration and pressure filtration methods for preparing porous fiber ceramics, achieving the preparation of porous fiber ceramic samples with uniform microstructure and high strength.

[0008] Mullite fiber porous ceramics are characterized by low pressure drop and high porosity. Their porous structure makes them lighter. At high temperatures, ρ-Al₂O₃ transforms into α-Al₂O₃ and reacts with silica powder to form mullite, which serves as the binder phase for the mullite fibers. Because both the fibers and the binder are mullite, they exhibit excellent creep resistance and thermal stability at high temperatures. Al(OH)₃ is cheaper than ρ-Al₂O₃ and can inhibit the hydration of ρ-Al₂O₃. During calcination, it thermally decomposes to produce H₂O, forming uniformly distributed micron-sized pores within the material and increasing its porosity. The γ-Al₂O₃ generated from calcined Al(OH)₃ is more reactive than ρ-Al₂O₃, promoting mullitization and low-temperature sintering. Silica powder can, to some extent, inhibit the excessive hydration of ρ-Al₂O₃ and can also react with Al₂O₃ during high-temperature sintering to form a mullite phase that binds the fibers, thus giving the fiber porous ceramic filter a certain strength.

[0009] In a preferred embodiment of the present invention, the amount of aluminum in p-Al2O3 accounts for 50% of the amount of aluminum in the aluminum source compound.

[0010] In a preferred embodiment of the present invention, γ-Al₂O₃ is obtained by calcining Al(OH)₃ in an air atmosphere. The γ-Al₂O₃ prepared by the present invention has high activity, large specific surface area, and a porous structure. Furthermore, its surface contains many unsaturated aluminum ions and hydroxyl groups.

[0011] In a preferred embodiment of the present invention, the mass ratio of p-Al2O3 to hydroxypropyl methylcellulose is 9~27:0.2. The addition of hydroxypropyl methylcellulose is mainly to adjust the viscosity of the slurry. Too much hydroxypropyl methylcellulose will lead to difficulties in molding, while too little hydroxypropyl methylcellulose will prevent the fibers from being evenly dispersed in the slurry and will result in low strength of the prepared green body.

[0012] In a preferred embodiment of the present invention, the mass ratio of p-Al2O3 to silica powder is 9~27:14. As the amount of silica powder added increases, the corundum phase of the product decreases, the mullite phase increases, the porosity decreases, and the bulk density increases; the Darcy permeability of the product also increases with the increase of silica powder content.

[0013] In a preferred embodiment of the present invention, the mass ratio of p-Al2O3 to mullite fibers is 9~27:25. As the number of mullite fibers increases, the bonding phase between fibers decreases, the sample morphology becomes more porous, and the porosity of the product increases, the bulk density decreases, and the Darcy permeability increases.

[0014] In a preferred embodiment of the present invention, the first temperature is 1400°C, and the holding time at the first temperature is 2 hours.

[0015] In a preferred embodiment of the present invention, the second temperature is 1500℃~1600℃, and the holding time at the second temperature is 5 hours. The present invention employs a staged heating process during the holding period to promote more uniform grain growth in the ceramic. During the first holding period, small grains grow rapidly while large grains grow slowly. After this stage, a second holding period is performed, resulting in more uniform grain size within the ceramic and promoting the full development and optimization of the mullite crystal phase. During the holding process, as the holding temperature increases, γ-Al2O3 gradually transforms into α-Al2O3 above 1200℃. The transformation becomes increasingly complete with rising temperature. Simultaneously, the increased temperature significantly accelerates the solid-phase diffusion rate of Al2O3 and SiO2, promoting the nucleation and growth of mullite.

[0016] The second objective of this invention is to provide a mullite fiber porous ceramic prepared by the above-described preparation method.

[0017] A third objective of this invention is to provide the application of the aforementioned mullite fiber porous ceramic as a flue gas filter material in the filtration of particulate matter in flue gas.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention allows Al(OH)3 or γ-Al2O3 to partially replace ρ-Al2O3. Al(OH)3 or γ-Al2O3 inhibits the hydration of ρ-Al2O3, decomposing it during calcination to generate water vapor, forming uniformly distributed micron-sized pores within the material, thus increasing the material's porosity. Furthermore, the use of gel casting ensures the slurry is liquid before the gel point, and after the gel point, a cross-linking reaction occurs instantaneously within the slurry, eliminating the directional flow of the binder and avoiding uneven binder distribution, thereby improving the strength of the fibrous porous ceramic. The hydration products generated by the reaction of ρ-Al2O3 with water at room temperature can form a network structure, imparting strength to the material and meeting the bonding stability requirements of fibrous porous ceramics. Additionally, the γ-Al2O3 generated by calcining Al(OH)3 in this invention is more reactive than ρ-Al2O3, promoting the formation of mullite. This invention uses Al(OH)3 or γ-Al2O3 to partially replace ρ-Al2O3 as a more active raw material. The decomposition of Al(OH)3 produces gas, which allows the ceramic to generate pores in situ, resulting in fibrous porous ceramics with higher porosity. At the same time, the use of a two-calcination process optimizes the pore structure inside the fibrous porous ceramics, thereby improving the filtration efficiency.

[0019] 2. Acrylamide, a commonly used organic gel system, is classified as a Group 2A carcinogen and poses a health risk. Therefore, this invention selects p-Al2O3, which does not generate harmful substances to the human body and the environment throughout the preparation process, as a gelling agent to prepare fiber porous ceramics. Attached Figure Description

[0020] Figure 1 A photograph of samples with different Al(OH)3 substitution amounts placed for the same period of time.

[0021] Figure 2 The images show the actual samples after calcination with different substitution amounts of Al(OH)3 and γ-Al2O3.

[0022] Figure 3 The XRD patterns of different samples are shown, where (a) represents different substitution amounts of γ-Al2O3 and (b) represents different substitution amounts of Al(OH)3.

[0023] Figure 4SEM images of samples with different substitution amounts of Al(OH)3 and γ-Al2O3 are shown below: (a1) is 0% Al(OH)3 at a scale bar of 50 μm, (a2) is 0% Al(OH)3 at a scale bar of 5 μm, (b1) is 25% Al(OH)3 at a scale bar of 50 μm, (b2) is 25% Al(OH)3 at a scale bar of 5 μm, (c1) is 50% Al(OH)3 at a scale bar of 50 μm, (c2) is 50% Al(OH)3 at a scale bar of 5 μm, (d1) is 75% Al(OH)3 at a scale bar of 50 μm, and (d2) is a scale bar of γ-Al2O3. (e1) is 75% Al(OH)3 at a scale of 50 μm, (e2) is 0% γ-Al2O3 at a scale of 5 μm, (f1) is 25% γ-Al2O3 at a scale of 50 μm, (f2) is 25% γ-Al2O3 at a scale of 5 μm, (g1) is 50% γ-Al2O3 at a scale of 50 μm, (g2) is 50% γ-Al2O3 at a scale of 5 μm, (h1) is 75% γ-Al2O3 at a scale of 50 μm, and (h2) is 75% γ-Al2O3 at a scale of 5 μm.

[0024] Figure 5 In the image, (a) is a representative SEM image of a sample with 50% Al(OH)3 substitution, (b) is the elemental spectrum, and the inset in (b) shows the percentage of each element, (c) is the elemental distribution map of Al, (d) is the elemental distribution map of O, (e) is the elemental distribution map of Si, (f) is the elemental spectrum of region 1 in (a), and the inset in (f) shows the percentage of each atom, and (g) is the elemental spectrum of region 2 in (a), and the inset in (g) shows the percentage of each atom.

[0025] Figure 6 The graphs show the linear shrinkage and mass loss rates of different samples during firing. (a) represents different substitution amounts of Al(OH)3, and (b) represents different substitution amounts of γ-Al2O3.

[0026] Figure 7 The figures show the apparent porosity and bulk density of different samples, where (a) represents different substitution amounts of Al(OH)3 and (b) represents different substitution amounts of γ-Al2O3.

[0027] Figure 8 The diagrams show the compressive strength of different samples, where (a) represents different substitution amounts of Al(OH)3 and (b) represents different substitution amounts of γ-Al2O3.

[0028] Figure 9 This is a schematic diagram of a permeability testing device.

[0029] Figure 10The diagram shows the permeability coefficients of different samples, where (a) represents different substitution amounts of Al(OH)3 and (b) represents different substitution amounts of γ-Al2O3.

[0030] Figure 11 The images show the actual samples after firing, where (a) shows a 50% Al(OH)3 substitution and (b) shows a 50% γ-Al2O3 substitution.

[0031] Figure 12 The XRD patterns of different samples are shown, where (a) represents a 50% Al(OH)3 substitution and (b) represents a 50% γ-Al2O3 substitution.

[0032] Figure 13 SEM images of 50% Al(OH)3 and γ-Al2O3 substitution samples at different firing temperatures are shown. (a1) is 50% Al(OH)3 at a scale bar of 50 μm, firing temperature 1400℃; (a2) is 50% Al(OH)3 at a scale bar of 5 μm, firing temperature 1400℃; (b1) is 50% Al(OH)3 at a scale bar of 50 μm, firing temperature 1500℃; (b2) is 50% Al(OH)3 at a scale bar of 5 μm, firing temperature 1500℃; (c1) is 50% Al(OH)3 at a scale bar of 50 μm, firing temperature 1600℃; (c2) is 50% Al(OH)3 at a scale bar of 5 μm, firing temperature 1600℃. %Al(OH)3, fired at 1600℃, (d1) is 50%γ-Al2O3 at a scale of 50μm, fired at 1400℃; (d2) is 50%γ-Al2O3 at a scale of 5μm, fired at 1400℃; (e1) is 50%γ-Al2O3 at a scale of 50μm, fired at 1500℃; (e2) is 50%γ-Al2O3 at a scale of 5μm, fired at 1500℃; (f1) is 50%γ-Al2O3 at a scale of 50μm, fired at 1600℃; (f2) is 50%γ-Al2O3 at a scale of 5μm, fired at 1600℃.

[0033] Figure 14 In the figure, (a) represents the firing linear shrinkage of the sample with 50% substitution of Al(OH)3 and γ-Al2O3, and (b) represents the mass loss rate of the sample with 50% substitution of Al(OH)3 and γ-Al2O3.

[0034] Figure 15 In the figure, (a) is the apparent porosity diagram of the sample with 50% substitution of Al(OH)3 and γ-Al2O3, and (b) is the bulk density diagram of the sample with 50% substitution of Al(OH)3 and γ-Al2O3.

[0035] Figure 16The compressive strength diagram of the sample with 50% substitution of Al(OH)3 and γ-Al2O3.

[0036] Figure 17 The permeability diagram is shown for the sample with 50% substitution of Al(OH)3 and γ-Al2O3.

[0037] Figure 18 The graph shows the relationship between the pressure drop of the sample and the air velocity.

[0038] Figure 19 This is a schematic diagram of a flue gas filtration testing device.

[0039] Figure 20 In the figure, (a) is the relationship between particulate matter concentration and filtration time; (b) is the average concentration of particulate matter in the size range of 0.3μm to 10μm within 30 min; (c) is the removal efficiency of 50% Al(OH)3 with a firing temperature of 1500℃ for particulate matter of different sizes in flue gas; (d) is the removal efficiency of 50% Al(OH)3 with a firing temperature of 1600℃ for particulate matter of different sizes in flue gas; (e) is the removal efficiency of 50% γ-Al2O3 with a firing temperature of 1500℃ for particulate matter of different sizes in flue gas; (f) is the removal efficiency of 50% γ-Al2O3 with a firing temperature of 1600℃ for particulate matter of different sizes in flue gas; and (g) is the relationship between pressure drop and filtration time for different samples.

[0040] Reference numerals: 1-Compressed air, 2-Digital pressure gauge, 3-Cavity, 4-Sealing device, 5-Sample, 6-Mass flow meter, 7-Simulated flue gas, 8-Pressure controller, 9-Dust particle counter. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] ρ-Al₂O₃ was purchased from China Aluminum Shandong Co., Ltd., with a specification of 8μm≤d. 50 ≤12μm; Al(OH)3 was purchased from Yangzhou Dilan Chemical Raw Materials Co., Ltd., with a specification of 800 mesh; silica powder was purchased from Yingge Ceramics Fused Minerals (Yingkou) Co., Ltd., with a specification of d 50=5.9μm; mullite fiber powder was purchased from Deqing Leijing Crystal Fiber Co., Ltd., with a specification of 3μm to 5μm; hydroxypropyl methylcellulose was purchased from Fuqiang Chemical Baoyi Building Materials, with a specification of >200,000 mPa·s; deionized water has a specification of 18 MΩ·cm. This invention uses mullite fiber, silica powder, and ρ-Al2O3 as main raw materials, replacing 0%, 25%, 50%, and 75% of the molar amount of ρ-Al2O3 with Al(OH)3 and γ-Al2O3, respectively, and introducing the additive hydroxypropyl methylcellulose to prepare mullite fiber porous ceramics. The substitution amounts described below refer to the amount of aluminum in Al(OH)3 or γ-Al2O3 accounting for 25% to 75% of the amount of aluminum in the aluminum source compound.

[0043] Example 1 Step 1: Weigh 27g of ρ-Al₂O₃, 13.76g of Al(OH)₃, and 14g of silica powder into a ball mill jar. Add agate balls as grinding media at a mass ratio of 3:1. After loading, seal the ball mill jar and place it into a ball mill. Set the ball mill speed to 300 rpm and mill for 2 hours. Start the ball mill to mix the materials and obtain a mixed powder for later use.

[0044] Step 2: Place a 250mL beaker into an ultrasonic cleaner, secure it with tape, add 75g of deionized water, and then add 0.2g of hydroxypropyl methylcellulose to the deionized water. Start the ultrasonic cleaner and electric stirrer, and stir for 10 minutes until the hydroxypropyl methylcellulose is completely dissolved. Next, add the ball-milled mixed powder to the beaker, and ultrasonically and mechanically stir for 10 minutes. Then add 25g of mullite fiber and continue ultrasonically and mechanically stirring for 20 minutes to ensure the mullite fiber is evenly dispersed, resulting in a uniformly stirred slurry.

[0045] Step 3: Pour the well-stirred slurry into the mold. Place the mold at room temperature until the sample is formed, then demold the sample. Place the demolded sample in an electric heating drying oven, first dry at 40°C until there is no moisture on the sample surface, then dry at 60°C for 2 hours, and then at 80°C for 2 hours to obtain the dried sample.

[0046] Step 4: Place the dried sample into a muffle furnace and calcine it in air atmosphere using a stepped heating method, from room temperature to 1400℃, with a heating rate of 5℃·min. -1 Hold at this temperature for 2 hours, from 1400℃ to 1500℃, with a heating rate of 2℃·min. -1 After heat treatment for 5 hours, mullite porous ceramics were obtained. The sample had a substitution percentage of 25% for Al(OH)3, which was recorded as 25%Al(OH)3.

[0047] Example 2 The difference from Example 1 is that in step 1, 18g of p-Al2O3 and 27.53g of Al(OH)3 are weighed.

[0048] The obtained sample has a substitution percentage of 50% for Al(OH)3. It is denoted as 50%Al(OH)3.

[0049] Example 3 The difference from Example 1 is that in step 1, 9g of p-Al2O3 and 41.30g of Al(OH)3 are weighed.

[0050] The obtained sample had a substitution percentage of 75% for Al(OH)3. This is denoted as 75%Al(OH)3.

[0051] Example 4 Step 1: Dissolve Al(OH)3 at 3℃·min -1 The temperature was increased to 700℃ at a certain heating rate, and calcined at 700℃ for 2 hours in air atmosphere to obtain highly active γ-Al2O3.

[0052] Step 2: Weigh 27g of ρ-Al₂O₃, 14g of silica powder, and 9g of γ-Al₂O₃ and place them in a ball mill jar. Add agate balls as grinding media at a mass ratio of 3:1. After loading, seal the ball mill jar and place it in a ball mill. Set the ball mill speed to 300 rpm and mill for 2 hours. Start the ball mill to mix the materials and obtain a mixed powder for later use.

[0053] Step 3: Place a 250mL beaker into an ultrasonic cleaner, secure it with tape, add 75g of deionized water, and add 0.2g of hydroxypropyl methylcellulose to the deionized water. Start the ultrasonic cleaner and electric stirrer, and stir for 10 minutes until the hydroxypropyl methylcellulose is completely dissolved. Then add the ball-milled mixed powder to the beaker, and ultrasonically and mechanically stir for 10 minutes. Add 25g of mullite fiber, and continue ultrasonically and mechanically stirring for 20 minutes to ensure that the mullite fiber is evenly dispersed, resulting in a well-mixed slurry.

[0054] Step 4: Pour the well-stirred slurry into the mold. Place the mold at room temperature until the sample is formed, then demold the sample. Place the demolded sample in an electric heating drying oven, first dry at 40°C until there is no moisture on the sample surface, then dry at 60°C for 2 hours, and then at 80°C for 2 hours to obtain the dried sample.

[0055] Step 5: Place the dried sample into a muffle furnace and calcine it in air atmosphere using a stepped heating method, from room temperature to 1400℃, with a heating rate of 5℃·min. -1 Hold at this temperature for 2 hours, from 1400℃ to 1500℃, with a heating rate of 2℃·min. -1After heating for 5 hours, a mullite porous ceramic was obtained. The sample had a γ-Al₂O₃ substitution percentage of 25%, denoted as 25% γ-Al₂O₃.

[0056] Example 5 The difference from Example 4 is that in step 2, 18g of p-Al2O3 and 18g of γ-Al2O3 are weighed.

[0057] The obtained sample had a 50% substitution percentage of γ-Al2O3. It is denoted as 50% γ-Al2O3.

[0058] Example 6 The difference from Example 4 is that in step 2, 9g of p-Al2O3 and 27g of γ-Al2O3 are weighed.

[0059] The obtained sample had a 75% substitution percentage of γ-Al2O3. This is denoted as 75% γ-Al2O3.

[0060] Comparative Example 1 Step 1: Weigh 36g of ρ-Al2O3 and 14g of silica powder into a ball mill jar. Add agate balls as grinding media at a mass ratio of 3:1. After loading, seal the ball mill jar and place it into a ball mill. Set the ball mill speed to 300 rpm and mill for 2 hours. Start the ball mill to mix the materials and obtain a mixed powder for later use.

[0061] Step 2: Place a 250mL beaker into an ultrasonic cleaner, secure it with tape, add 75g of deionized water, and then add 0.2g of hydroxypropyl methylcellulose to the deionized water. Start the ultrasonic cleaner and electric stirrer, and stir for 10 minutes until the hydroxypropyl methylcellulose is completely dissolved. Next, add the ball-milled mixed powder to the beaker, and ultrasonically and mechanically stir for 10 minutes. Then add 25g of mullite fiber and continue ultrasonically and mechanically stirring for 20 minutes to ensure the mullite fiber is evenly dispersed, resulting in a uniformly stirred slurry.

[0062] Step 3: Pour the well-stirred slurry into the mold. Place the mold at room temperature until the sample is formed, then demold the sample. Place the demolded sample in an electric heating drying oven, first dry at 40°C until there is no moisture on the sample surface, then dry at 60°C for 2 hours, and then at 80°C for 2 hours to obtain the dried sample.

[0063] Step 4: Place the dried sample into a muffle furnace and calcine it in air atmosphere using a stepped heating method, from room temperature to 1400℃, with a heating rate of 5℃·min. -1 Hold at this temperature for 2 hours, from 1400℃ to 1500℃, with a heating rate of 2℃·min. -1 After heat preservation for 5 hours, mullite porous ceramics were obtained.

[0064] It should be noted that when the substitution amount of Al(OH)3 or γ-Al2O3 is 0, the products are the same. For the sake of performance comparison, the following content will be described separately with the substitution amount of Al(OH)3 being 0% and the substitution amount of γ-Al2O3 being 0%. Al(OH)3 substitution amount of 0 is recorded as 0%Al(OH)3, and γ-Al2O3 substitution amount of 0 is recorded as 0%γ-Al2O3.

[0065] Table 1 shows the demolding times of samples with different Al(OH)3 and γ-Al2O3 substitution amounts in Examples 1 to 6. The morphology of the Al(OH)3 substitution group samples after being placed at room temperature for 1 hour is shown in Table 1. Figure 1 As shown. (Combined with Table 1 and...) Figure 1 It can be demonstrated that ρ-Al₂O₃ hydrates rapidly, resulting in faster setting and demolding times for samples with higher ρ-Al₂O₃ content. The addition of Al(OH)₃ inhibits hydration. The reason ρ-Al₂O₃ affects setting and demolding time is that it undergoes a hydration reaction, generating easily gelling alumina hydrates, which promotes the transformation of the slurry from a Newtonian fluid to a non-Newtonian fluid. Simultaneously, after hydration, free water in the slurry is converted into bound water, further promoting slurry setting and shortening demolding time.

[0066] Table 1 Demolding time of samples with different Al(OH)3 and γ-Al2O3 substitution amounts

[0067] The states of samples after calcination with different substitution amounts of Al(OH)3 and γ-Al2O3 are as follows: Figure 2 As shown, it can be seen that with the increase of Al(OH)3 and γ-Al2O3 substitution, the surface roughness of the samples increases and the integrity decreases. In particular, the two groups of samples with 0% substitution showed a small number of microcracks at the edges after calcination. It should be noted that... Figure 2 To avoid sample confusion during the experiment, different samples were labeled. The XRD patterns of mullite fiber porous ceramics prepared with different substitution amounts of Al(OH)3 and γ-Al2O3 are shown below. Figure 3As shown, both groups of samples with four different substitution amounts can generate mullite phase at a firing temperature of 1500℃, and the characteristic diffraction peaks of mullite are obvious, indicating good crystallinity. As the substitution amount of Al(OH)3 and γ-Al2O3 increases from 0% to 75%, the intensity of the mullite diffraction peaks gradually increases. During the sample firing process, Al(OH)3 decomposes into γ-Al2O3 at 700℃. γ-Al2O3 has a higher activity than ρ-Al2O3, making it more likely to react with silica powder to form mullite. Simultaneously, some diffraction peaks of corundum are also present. This may be because the molar ratio of Al2O3 to SiO2 in the raw material is equal to the theoretical chemical formula of mullite, 3Al2O3·2SiO2. When mullite crystallizes from the melt, some Al2O3 dissolves, preventing the complete formation of mullite from Al2O3.

[0068] The microstructures of mullite fiber porous ceramics prepared with different substitution amounts of Al(OH)3 and γ-Al2O3 are as follows: Figure 4 As shown. By Figure 4 As shown in (b1) and (b2), when the Al(OH)3 substitution amount is 25%, the sample structure becomes more loose, and the internal porosity increases. With the Al(OH)3 substitution amount increasing to 50%, the number of lamellar structures inside the mullite fiber porous ceramic increases significantly, and the size gradually increases from 5 μm to over 10 μm, with tiny groove-like patterns appearing on its surface. When the Al(OH)3 substitution amount is 75%, the mullite formation reaction is more complete, the particle size decreases significantly, the number of lamellar crystals decreases greatly, the neck bonding between particles becomes tighter, and the pore size decreases. When γ-Al2O3 replaces ρ-Al2O3, at a substitution amount of 25%, the internal pores of the sample increase, and the lamellar particles overlap, making the sample structure relatively loose. Figure 4 In samples (h1) and (h2), when the γ-Al2O3 substitution amount is 75%, it is evident that the number of small-sized particles increases significantly, the material density is significantly improved, and the pore size becomes smaller. Furthermore, comparing the Al(OH)3 and γ-Al2O3 substituted samples, it can be seen that the γ-Al2O3 group has a higher proportion of small-sized particles than the Al(OH)3 substituted group.

[0069] To confirm the composition of the lamellar structure, micro-area energy dispersive spectroscopy (EDS) was performed on a sample with 50% Al(OH)3 substitution. Figure 5 In (a), a relatively flat lamellar structure can be observed, with a large number of irregular granular products attached to it, containing three elements: Al, O, and Si, with Al being the most densely distributed. According to Figure 5 The data in Table (b) show that the atomic molar ratio of Al to Si in the sample is close to 3:1, which is consistent with the theoretical ratio of mullite. Point scan analysis was performed on regions 1 and 2, and the results are as follows... Figure 5As shown in (f) and (g), it can be seen that the O and Si contents increase and the Al content decreases in region 2, with the Al:Si ratio becoming closer to 3:1, indicating that the lamellar structure is mullite formed by the reaction. Combined with... Figure 4 It can be observed that the surface texture of the lamellar crystals is distributed in an irregular network or linear pattern. This may be because during the calcination process, Al(OH)3 and ρ-Al2O3 decompose to produce gases, which leads to the formation of groove-like textures on the crystal surface.

[0070] The changes in linear shrinkage and mass loss rate of mullite fiber porous ceramics after sintering under different substitution amounts of Al(OH)3 and γ-Al2O3 are as follows: Figure 6 As shown. By Figure 6 As shown in (a), with the increase of Al(OH)3 substitution, the firing linear shrinkage of the sample gradually decreases, while the firing mass loss rate continues to increase. Pure ρ-Al2O3 transforms into α-Al2O3 at temperatures of 950–1200 °C, a process accompanied by significant volume shrinkage. When Al(OH)3 is substituted at 25%, Al(OH)3 decomposes into γ-Al2O3 at 700 °C, and further transforms into α-Al2O3 with increasing temperature. These two reactions are accompanied by severe volume shrinkage, but the H2O produced by the decomposition of Al(OH)3 causes volume expansion, inhibiting the firing shrinkage of the sample. Consequently, the firing linear shrinkage of the sample with 25% Al(OH)3 substitution is not significantly different from that of pure ρ-Al2O3. With the increase of Al(OH)3 substitution, its decomposition leads to increasingly greater mass loss of the sample. At the same time, the increased porosity produced by decomposition dominates the inhibition of firing linear shrinkage, resulting in a decrease in shrinkage rate and an increase in mass loss rate. Figure 6 As shown in (b), with the increase of γ-Al2O3 substitution, the firing linear shrinkage of the sample first decreases and then increases, reaching its minimum when the γ-Al2O3 substitution is 50%. This is because γ-Al2O3 densifies the sample, reducing the firing linear shrinkage. When there is too much γ-Al2O3, uneven phase distribution occurs during sintering, causing stress concentration and thus a slight increase in linear shrinkage. At a γ-Al2O3 substitution of 25%, the firing mass loss rate increases compared to 0% substitution. With further increases in γ-Al2O3 substitution, the firing mass loss rate decreases. This is because ρ-Al2O3 powder undergoes a hydration reaction at room temperature to form pyrite and boehmite sols. These products dehydrate during drying and calcination, resulting in mass loss. As the γ-Al2O3 substitution increases, the amount of water removed during calcination decreases, thus reducing the mass loss rate.

[0071] Apparent porosity and bulk density of samples with different substitution amounts of Al(OH)3 and γ-Al2O3 are as follows: Figure 7 As shown. By Figure 7As shown in (a) of the figure, when the Al(OH)3 substitution amount is 25%, compared with the sample containing pure ρ-Al2O3 powder, the apparent porosity is slightly increased and the bulk density is decreased. This is because the added Al(OH)3 decomposes to produce gas, which increases the apparent porosity. However, as the Al(OH)3 substitution amount increases, the apparent porosity of the sample gradually decreases and the bulk density gradually increases. This is because the γ-Al2O3 particles generated by the decomposition of Al(OH)3 are finer and can fill the pores between fibers. At the same time, the highly active γ-Al2O3 is more likely to react with silica powder to form mullite, promoting sintering between particles and thus densifying the sample. In Figure 7(b), when the γ-Al2O3 substitution amount is 25%, compared with the sample containing pure ρ-Al2O3 powder, the apparent porosity is slightly increased and the bulk density is decreased. This is because ρ-Al2O3 still dominates the system at this time. ρ-Al2O3 loses water during calcination, thus causing an increase in porosity. With increasing γ-Al₂O₃ substitution, it fills the pores between fibers, promoting interparticle sintering and thus causing a continuous increase in the sample's bulk density. The compressive strength variation of mullite fiber porous ceramics under different substitution amounts of Al(OH)₃ and γ-Al₂O₃ is shown in the figure below. Figure 8 As shown. Compressive strength refers to the ability of a material to withstand pressure. In this invention, the compressive strength of the sample is calculated using the maximum pressure that a unit area of ​​the mullite fiber porous ceramic sample can withstand. As the substitution amount of Al(OH)3 and γ-Al2O3 increases, γ-Al2O3 fills the pores between fibers during calcination, making the connection between particles increasingly tighter and increasing the density of the sample. This results in a consistent change pattern between compressive strength and bulk density.

[0072] use Figure 9 The instrument shown is used to test the Darcy permeability of a sample. It consists of four parts: a gas generator, a pressure testing section, a flow testing section, and a sample mounting section. During the test, compressed air 1 passes through sample 5. The pressure difference of compressed air 1 before and after passing through the sample is measured by a digital pressure gauge 2, and the volumetric flow rate of the gas through sample 5 is measured by a mass flow meter 6. The pressure gradient of sample 5 is also shown. and the volumetric flow rate of compressed air 1 through sample 5 v s The calculations are performed using the following formulas: ; ; In the formula: P i P is the air pressure entering the sample. o The air pressure after the sample is removed; P is the air pressure corresponding to the air flow rate; L is the thickness of the sample; Q v denoted as , where is the volumetric flow rate of compressed air; A is the permeation area of ​​compressed air through the sample.

[0073] By fitting the obtained pressure gradient and volumetric flow rate using Darcy's law, the Darcy permeability coefficient k1 of the sample can be obtained.

[0074] ; In the formula: The pressure gradient represents the direction of the flow velocity; η represents the viscosity of the compressed air. v s This indicates the volumetric flow rate of compressed air through the sample. k 1 represents the Darcy permeability coefficient.

[0075] The permeability coefficient variation of mullite fiber porous ceramics under different substitution amounts of Al(OH)3 and γ-Al2O3 is as follows: Figure 10 As shown, the Darcy permeability coefficient is obtained by mathematically fitting the pressure drop and flow velocity using the Darcy formula. k 1. By Figure 10 As shown in (a), the permeability coefficient of the sample first increases and then decreases with the increase of Al(OH)3 substitution. At 0% substitution, pure ρ-Al2O3 powder directly participates in sintering to form the mullite phase, resulting in relatively dense particle packing. When the Al(OH)3 substitution is 25%, aluminum hydroxide decomposes to form γ-Al2O3 and releases water vapor, forming micropores, causing a slight increase in the sample's permeability coefficient. When the Al(OH)3 substitution is 50%, more Al(OH)3 decomposes, leading to a significant increase in porosity. However, the γ-Al2O3 generated from the decomposition fills some of the fiber gaps. With proper sintering temperature control, the increase in open porosity dominates, thus causing an increase in permeability coefficient. When the Al(OH)3 substitution is 75%, excess active γ-Al2O3 undergoes a mullite formation reaction, promoting interparticle sintering and causing a significant decrease in permeability coefficient. Figure 10 In (b), as the amount of γ-Al₂O₃ substitution increases, the permeability of the sample decreases from 8.42 × 10⁻⁶. -13 m 2 Reduced to 2.37×10 -14 m 2 At 0% substitution, pure ρ-Al2O3 powder directly participates in sintering to form the mullite phase. As the substitution amount of γ-Al2O3 increases, it can fill the pores between fibers. At the same time, the highly active γ-Al2O3 is more likely to react with silica powder to form mullite, promoting interparticle sintering, thereby densifying the sample and causing a decrease in the permeability coefficient.

[0076] This invention analyzes the phase composition, microstructure, firing linear shrinkage, firing mass loss, apparent porosity, bulk density, compressive strength, and Darcy permeability of mullite fiber porous ceramics with different substitution amounts of Al(OH)3 and γ-Al2O3. The results show that when the Al(OH)3 substitution amount is 50%, the apparent porosity of the porous ceramic material is 59.35%, the compressive strength is 8.98 MPa, and the permeability is 1.27 × 10⁻⁶. -12 m 2 When the γ-Al₂O₃ substitution amount is 50%, the apparent porosity of the porous ceramic material is 60.60%, the compressive strength is 5.10 MPa, and the Darcy permeability coefficient is 1.13 × 10⁻⁶. -13 m 2 The subsequent experiments will be conducted with Al(OH)3 substitution at 50% and γ-Al2O3 substitution at 50%. When studying the effect of temperature on mullite fiber porous ceramics, step 4 involves a single temperature increase.

[0077] Example 7 Step 1: Weigh 18g of ρ-Al₂O₃, 27.53g of Al(OH)₃, and 14g of silica powder into a ball mill jar. Add agate balls as grinding media at a mass ratio of 3:1. After loading, seal the ball mill jar and place it into a ball mill. Set the ball mill speed to 300 rpm and mill for 2 hours. Start the ball mill to mix the materials and obtain a mixed powder for later use.

[0078] Step 2: Place a 250mL beaker into an ultrasonic cleaner, secure it with tape, add 75g of deionized water, and then add 0.2g of hydroxypropyl methylcellulose to the deionized water. Start the ultrasonic cleaner and electric stirrer, and stir for 10 minutes until the hydroxypropyl methylcellulose is completely dissolved. Next, add the ball-milled mixed powder to the beaker, and ultrasonically and mechanically stir for 10 minutes. Then add 25g of mullite fiber and continue ultrasonically and mechanically stirring for 20 minutes to ensure the mullite fiber is evenly dispersed, resulting in a uniformly stirred slurry.

[0079] Step 3: Pour the well-stirred slurry into the mold. Place the mold at room temperature until the sample is formed, then demold the sample. Place the demolded sample in an electric heating drying oven, first dry at 40°C until there is no moisture on the sample surface, then dry at 60°C for 2 hours, and then at 80°C for 2 hours to obtain the dried sample.

[0080] Step 4: Place the dried sample into a muffle furnace and heat from room temperature to 1400℃ at a rate of 5℃·min. -1 After heating for 2 hours, a mullite porous ceramic was obtained. The sample was 50% Al(OH)3 substituted.

[0081] Example 8 The difference from Example 7 is that in step 4, the temperature is raised to 1450°C.

[0082] Example 9 The difference from Example 7 is that in step 4, the temperature is raised to 1500°C. This is denoted as 50%Al(OH)3 at 1500°C.

[0083] Example 10 The difference from Example 7 is that in step 4, the temperature is raised to 1550°C.

[0084] Example 11 The difference from Example 7 is that in step 4, the temperature is raised to 1600°C. This is denoted as 50%Al(OH)3 at 1600°C.

[0085] Example 12 Step 1: Dissolve Al(OH)3 at 3℃·min -1 The temperature was increased to 700℃ at a certain heating rate, and calcined at 700℃ for 2 hours to obtain highly active γ-Al2O3.

[0086] Step 2: Weigh 18g of ρ-Al₂O₃, 14g of silica powder, and 18g of γ-Al₂O₃ and place them in a ball mill jar. Add agate balls as grinding media at a mass ratio of 3:1. After loading, seal the ball mill jar and place it in a ball mill. Set the ball mill speed to 300 rpm and mill for 2 hours. Start the ball mill to mix the materials and obtain a mixed powder for later use.

[0087] Step 3: Place a 250mL beaker into an ultrasonic cleaner, secure it with tape, add 75g of deionized water, and add 0.2g of hydroxypropyl methylcellulose to the deionized water. Start the ultrasonic cleaner and electric stirrer, and stir for 10 minutes until the hydroxypropyl methylcellulose is completely dissolved. Then add the ball-milled mixed powder to the beaker, and ultrasonically and mechanically stir for 10 minutes. Add 25g of mullite fiber, and continue ultrasonically and mechanically stirring for 20 minutes to ensure that the mullite fiber is evenly dispersed, resulting in a well-mixed slurry.

[0088] Step 4: Pour the well-stirred slurry into the mold. Place the mold at room temperature until the sample is formed, then demold the sample. Place the demolded sample in an electric heating drying oven, first dry at 40°C until there is no moisture on the sample surface, then dry at 60°C for 2 hours, and then at 80°C for 2 hours to obtain the dried sample.

[0089] Step 5: Place the dried sample into a muffle furnace and heat it in air at a rate of 5°C / min from room temperature to 1400°C. -1 After heating for 2 hours, a mullite porous ceramic was obtained. The sample had a γ-Al2O3 substitution percentage of 50%.

[0090] Example 13 The difference from Example 12 is that in step 4, the temperature is raised to 1450°C.

[0091] Example 14 The difference from Example 12 is that in step 4, the temperature is raised to 1500°C. This is denoted as 50% γ-Al₂O₃ at 1500°C.

[0092] Example 15 The difference from Example 12 is that in step 4, the temperature is raised to 1550°C.

[0093] Example 16 The difference from Example 12 is that in step 4, the temperature is raised to 1600°C, which is recorded as 50% γ-Al2O3 1600°C.

[0094] The following experiments investigated the effect of temperature on the properties of mullite fiber porous ceramics by calcining samples with Al(OH)3 and γ-Al2O3 replacing 50% of the samples at 1400℃, 1450℃, 1500℃, 1550℃, and 1600℃.

[0095] Samples with 50% substitution of Al(OH)3 and γ-Al2O3 were calcined at 1400℃, 1450℃, 1500℃, 1550℃, and 1600℃, respectively. The sample states are as follows. Figure 11 As shown, when both groups of samples were fired at 1600℃, large cracks appeared at the sample edges, causing the samples to break. The γ-Al₂O₃ substituted sample was more intact than the Al(OH)₃ substituted sample. It should be noted that... Figure 11 In order to avoid sample confusion, labels were used. Figure 11 Each row in the diagram represents multiple parallel samples prepared under the same conditions.

[0096] The XRD patterns of samples with 50% Al(OH)3 and γ-Al2O3 substitution were obtained by calcining at 1400℃, 1500℃, and 1600℃, respectively. Figure 12 As shown, the sample with 50% Al(OH)3 and γ-Al2O3 substitution still contained a small amount of quartz phase and some corundum phase at a firing temperature of 1400℃. When the firing temperature increased to 1500℃, the diffraction peaks of the quartz phase disappeared, and the intensity of the diffraction peaks of the corundum phase also gradually weakened or disappeared with the increase of firing temperature. With the increase of firing temperature, the diffraction peak intensity of mullite in both groups of samples gradually increased. γ-Al2O3 gradually transforms into α-Al2O3 above 1200℃, and the transformation becomes more and more complete with the increase of temperature. At 1600℃, the proportion of α-Al2O3 increases significantly. At the same time, the increase of temperature significantly accelerates the solid-phase diffusion rate of Al2O3 and SiO2, promoting the nucleation and growth of mullite.

[0097] The microstructures of mullite fiber porous ceramics prepared at different firing temperatures using Al(OH)3 and γ-Al2O3 substitutes are as follows: Figure 13 As shown. From Figure 13 It can be seen that the particle packing of the γ-Al₂O₃ substituted samples is more compact than that of the Al(OH)₃ substituted group. From... Figure 13 As can be seen from (a1) to (c2), the sample with 50% Al(OH)3 substitution exhibits a relatively loose structure and inconsistent pore sizes when fired at 1400℃. The sample fired at 1500℃ shows enhanced neck connections between particles, with some pores filled by particles. However, the overlapping of the lamellar composite crystals slightly increases the pore size, resulting in a more pronounced pore structure. The sample fired at 1600℃ shows a significant reduction in the number of lamellar crystals, decreased particle size differences, further enhanced neck connections blurring particle boundaries, and smaller particles filling the pores, leading to a more uniform pore size and a relatively continuous structure. Based on... Figure 13 In (d1) to (f2), the internal pore size of the sample fired at 1400℃ is smaller and more uniform. At 1500℃ and 1600℃, the degree of bonding between sample particles is enhanced, and some small pores connect to form larger pores, resulting in uneven pore size.

[0098] The changes in linear shrinkage and mass loss rate of mullite fiber porous ceramics sintered with Al(OH)3 and γ-Al2O3 at a 50% substitution rate are as follows: Figure 14 As shown. By Figure 14 As shown in (a), the linear shrinkage rates of Al(OH)3 and γ-Al2O3 in the 50% substitution sample continuously increase with increasing firing temperature. ρ-Al2O3 transforms into α-Al2O3 at temperatures between 950 and 1200 °C, while aluminum hydroxide first decomposes into γ-Al2O3 and then further transforms into α-Al2O3; these transformation processes are accompanied by volume shrinkage. With increasing firing temperature, the reactions become more complete, thus leading to a continuous increase in the linear shrinkage rate of the sample. Figure 14 As shown in (b), with increasing firing temperature, the firing mass loss rate of the sample with 50% Al(OH)3 substitution remained basically between 17% and 18%, while the firing mass loss rate of the sample with 50% γ-Al2O3 substitution fluctuated more, but still remained between 6% and 11%. This is because the decomposition and water loss of Al(OH)3 and the dehydration of ρ-Al2O3 hydration products were completed before 1400℃. Within the range of 1400℃ to 1600℃, the mullite + α-Al2O3 + SiO2 material system was in a thermodynamically stable state, with no reaction resulting in the formation of volatile substances.

[0099] The changes in apparent porosity and bulk density of mullite fiber porous ceramics with 50% substitution of Al(OH)3 and γ-Al2O3 are as follows: Figure 15 As shown, the apparent porosity of the two groups of samples with 50% Al(OH)3 substitution and 50% γ-Al2O3 substitution was the highest at 1400℃, at 63.01% and 60.72%, respectively. With increasing firing temperature, the apparent porosity showed a gradual decreasing trend, reaching 56.59% and 53.38% at 1600℃, respectively. The bulk density of the samples was the lowest at 1400℃, at 1.11 g·cm³. -3 and 1.15 g·cm -3 As the firing temperature increased, the bulk density of both groups of samples gradually increased, reaching a maximum of 1.32 g·cm³ at a firing temperature of 1600℃. -3 and 1.40 g·cm -3 This is because as the firing temperature increases, the particles in the green body gradually rearrange, bonding occurs at the particle contact points, the solid-phase diffusion rate increases, and more mullite phase is formed, thus enhancing the densification of the sample. The reason why the apparent porosity of the 50% Al(OH)3 substitution group is higher than that of the 50% γ-Al2O3 substitution group, while its bulk density is lower, is that Al(OH)3 decomposes during firing to produce H2O, resulting in increased apparent porosity and a looser sample structure. In contrast, the 50% γ-Al2O3 substitution group produces less H2O from the dehydration of ρ-Al2O3 hydration products. The directly added γ-Al2O3 does not require decomposition and has a finer particle size, which can fill the pores between fibers. Furthermore, the highly reactive γ-Al2O3 reacts more readily with silica powder to form mullite, promoting interparticle sintering and thus densifying the sample, resulting in a higher bulk density.

[0100] The compressive strength of mullite fiber porous ceramics with 50% substitution of Al(OH)3 and γ-Al2O3 is as follows: Figure 16 As shown. By Figure 16 It can be seen that when the firing temperature is 1400℃, the compressive strength of both groups of samples is at its minimum, at 3.17 MPa and 4.44 MPa, respectively. As the temperature increases, the compressive strength of both groups of samples gradually increases, reaching maximum values ​​of 9.52 MPa and 15.53 MPa, respectively, at 1600℃. During this process, the compressive strength of both groups of samples shows a significant increase between 1500℃ and 1600℃. This is mainly because the higher firing temperature accelerates the transfer and migration of particles in the samples, transforming the mass transfer mechanism from diffusion to a combination of diffusion and gas-phase mass transfer. This increases the contact area between particles and makes the interparticle bonding more compact, thus significantly improving the compressive strength of the samples.

[0101] Darcy permeability of mullite fiber porous ceramics with 50% substitution of Al(OH)3 and γ-Al2O3 k 1. Figure 17As shown, the Darcy permeability coefficient of the sample with 50% Al(OH)3 substitution gradually increases with increasing firing temperature, from 4.4 × 10⁻⁶ at 1400℃. -13 m 2 1.3 × 10⁻⁶ at 1600℃ -12 m 2 The Darcy permeability coefficient of the sample with 50% γ-Al₂O₃ substitution did not change significantly overall, from 1400℃ to 1600℃. k 1 is 3.0 × 10 -13 m 2 3.1×10 -13 m 2 3.9×10 -13 m 2 4.7×10 -13 m 2 3.3×10 -13 m 2 Based on SEM image analysis, aluminum hydroxide decomposes to produce water vapor during calcination. As the calcination temperature increases, the residual gas expands and permeates the pores, thereby increasing the permeation channels and causing the Darcy permeability coefficient of the sample with 50% Al(OH)3 substitution to increase. γ-Al2O3 does not decompose to produce gas, and its disturbance to the pore structure is relatively small, resulting in little overall change in the Darcy permeability coefficient of the sample.

[0102] This invention involves calcining samples with 50% Al(OH)3 and γ-Al2O3 substitution at 1400℃, 1450℃, 1500℃, 1550℃, and 1600℃ to investigate the effects of temperature on the microstructure and macroscopic properties of the materials. With increasing calcination temperature, the apparent porosity of both groups of samples decreased, the bulk density gradually increased, the densification of the samples enhanced, and the compressive strength of both groups also continuously increased. Furthermore, the integrity, bulk density, and compressive strength of the γ-Al2O3 group were superior to those of the Al(OH)3 substitution group. The Darcy permeability coefficient of the sample with 50% Al(OH)3 substitution showed a gradually increasing trend, while the Darcy permeability coefficient of the sample with 50% γ-Al2O3 substitution did not change significantly overall, but was lower than that of the 50% Al(OH)3 substitution group.

[0103] The following study investigates the flue gas filtration behavior of mullite fiber porous ceramics. Figure 19 The flue gas filtration device shown was used to conduct flue gas filtration experiments on mullite fiber porous ceramic materials obtained by calcination at 1500℃ and 1600℃ with 50% substitution of Al(OH)3 and γ-Al2O3. Figure 18This paper presents the relationship between the pressure drop and air velocity of four samples fired at 1500℃ (Al(OH)3), 1600℃ (Al(OH)3), 1500℃ (γ-Al2O3), and 1600℃ (γ-Al2O3). Based on the obtained data, a linear fit was performed, and the calculated air permeability was 6150.4 L·m⁻¹. -2 ·h -1 ·kPa -1 11937.4 L·m -2 ·h -1 ·kPa -1 3161.3 L·m -2 ·h -1 ·kPa -1 1917.2 L·m -2 ·h -1 ·kPa -1 As can be seen, the sample with 50% Al(OH)3 substitution and fired at 1600℃ had the highest air permeability, while the sample with 50% γ-Al2O3 substitution and fired at 1600℃ had the lowest air permeability. Furthermore, the air permeability of the Al(OH)3 group was higher than that of the γ-Al2O3 group, consistent with the previous trends in porosity and Darcy's permeability coefficient. This is because Al(OH)3 decomposes during calcination, producing gas that results in relatively loose particle packing. When the firing temperature rises to 1600℃, some micropores connect to form larger pores. γ-Al2O3 particles are finer, resulting in more compact particle packing, thus leading to its lower air permeability. The flue gas filtration experiment was conducted using... Figure 19 The instrument shown is used for measurement. Its main working principle is through measurement... Figure 19 The pressure difference between the two cavities 3, the gas flow rate at the outlet, and the number of particles are used to calculate the filtration efficiency and other performance characteristics of the sample. The compressed air 1 introduced on the far left is mainly achieved using a vacuum machine. The simulated smoke 7 is the smoke produced by burning mosquito coils. The sample 5 is placed between the two cavities 3 to act as a filter, and both cavities 3 are well sealed. The smoke produced by burning mosquito coils contains particles of various sizes; therefore, in this invention, the smoke produced by burning mosquito coils is used as the smoke source in the smoke filtration. The smoke produced by burning mosquito coils contains particles ranging from smaller than 0.3 μm to larger than 10 μm, with the vast majority of particles smaller than 10 μm. Therefore, a dust particle counter 9 is used during the measurement process to count particles with a diameter of 0.3–10 μm in the smoke. The dust particle counter 9 can simultaneously measure the concentration of particles of 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2.5 μm, and 10 μm. The pressure drop of the smoke before and after passing through the sample can be measured using the instrument. The removal efficiency E of particles with diameters ranging from 0.3 μm to 10 μm and the gas permeability J in the experiment were calculated using the following formulas: ; In the formula: C1 represents the concentration of particulate matter before filtration; C2 represents the concentration of particulate matter after filtration.

[0104] ; In the formula: Qv The volumetric flow rate is represented by S, the filtration area is represented by ΔP, the pressure drop of the gas through the sample is represented by ΔP, and the unit of permeability J is L·h. -1 ·m -2 ·kPa -1 .

[0105] The experiment used Figure 19 The flue gas filtration instrument shown was used to perform a flue gas filtration test on the sample, and the results are as follows: Figure 20 As shown. Figure 20 Figure (a) shows the relationship between particulate matter concentration and filtration time in the flue gas from mosquito coil combustion. As can be seen from the figure, the particulate matter concentration in the flue gas from 0.3 μm to 10 μm remains relatively stable within a filtration time of 30 min, which proves that the flue gas produced by mosquito coil combustion can simulate stable dusty air for flue gas filtration testing of the sample. Figure 20 (b) in the figure represents the average concentration of particulate matter in the 0.3 μm to 10 μm size range over 30 minutes. Figure 20 As can be seen, the concentration of particulate matter larger than 0.3 μm in the smoke produced by burning mosquito coils is approximately 9.1 × 10⁻⁶. 5 L -1 More than 60% of the particles are between 0.5 μm and 1 μm in size, with only about 10% larger than 1 μm. This proves that the majority of the smoke produced by burning mosquito coils consists of submicron particles, making it suitable as a source of dusty air for filtration experiments involving submicron particles. Figure 20 In the figure, (c) to (f) represent the removal efficiency of 0.3 μm to 10 μm particles by four samples fired at 1500℃ and 1600℃ within a filtration time of 30 min. Figure 20 In the figure, (d) represents the relationship between the filtration pressure drop of each sample and the filtration time. The first filtration pressure drop was recorded 1 minute after the start of the filtration experiment, and subsequent recordings were made at 1-minute intervals. Each sample had a total of 30 filtration pressure drop values ​​over a 30-minute filtration period. Figure 20It can be seen that the samples with 50% Al(OH)3 substitution and calcination at 1500℃ and the samples with 50% γ-Al2O3 substitution and calcination at 1500℃ both achieved removal efficiencies of over 99.5% for all particles larger than 0.3 μm in the flue gas, with the removal efficiency gradually increasing with filtration time. However, their filtration pressure drops were relatively high, fluctuating around 17.5 kPa and 8.4 kPa, respectively. The sample with 50% Al(OH)3 substitution and calcination at 1600℃ achieved removal efficiencies of over 99.4% for particles of all sizes in the flue gas, with stable filtration efficiency within 30 minutes and a stable filtration pressure drop of 3.0 kPa. The sample with 50% γ-Al2O3 substitution and calcination at 1600℃ had lower removal efficiencies for particulate matter in the flue gas. Its removal efficiency for particles larger than 0.5 μm remained stable at over 97%, while its removal efficiency for particles in the 0.3 μm to 0.5 μm size range fluctuated significantly and showed a decreasing trend over time. Figure 20 As shown in (d), the filtration pressure drop of the 50% Al(OH)3 substitution group and the 50% γ-Al2O3 substitution group under calcination at 1600℃ was lower and more stable than that under calcination at 1500℃. At the same calcination temperature, the Al(OH)3 substitution group sample had a lower filtration pressure drop than the γ-Al2O3 substitution group sample. This may be because the sintering degree of the sample is higher at 1600℃. Combined with the scanning image, it can be seen that the smaller pores inside the sample are coalesced to form larger pores, resulting in a lower pressure drop when flue gas passes through the sample. Simultaneously, high-temperature calcination leads to stronger neck connections between sample particles, which can withstand airflow impact and maintain structural stability. Therefore, the filtration pressure drop changes stably with filtration time. During calcination, Al(OH)3 decomposes to produce gas, resulting in relatively loose particle packing. In contrast, the γ-Al2O3 direct substitution particles have a finer initial particle size, making it easier for particles to sinter and form sintering necks, thus densifying the sample and resulting in a higher filtration pressure drop. In summary, the sample prepared under the conditions of 50% Al(OH)3 substitution and calcination at 1600℃ achieved a removal efficiency of over 99.5% for 0.3μm to 0.5μm particles in flue gas, and the filtration pressure drop remained stable at 3.0kPa within 30 minutes. It has the advantages of high filtration accuracy and low pressure drop in removing submicron particles from the air.

[0106] This invention uses the flue gas generated by burning mosquito coils to simulate dusty air. Flue gas filtration experiments were conducted on four samples fired at 1500℃ and 1600℃ with 50% substitution of Al(OH)3 and γ-Al2O3. The results show that the two Al(OH)3 samples and the γ-Al2O3 sample fired at 1500℃ achieved a removal efficiency of over 99.5% for all particles larger than 0.3μm in the flue gas. The γ-Al2O3 sample fired at 1600℃ had a lower removal efficiency for particulate matter in the flue gas, with the overall removal efficiency for particles larger than 0.3μm fluctuating around 95%. The filtration pressure drop of the two samples fired at 1600℃ was lower and more stable than that of the samples fired at 1500℃. At the same firing temperature, the Al(OH)3 substitution group had a lower filtration pressure than the γ-Al2O3 substitution group. The sample prepared under the conditions of 50% Al(OH)3 and calcination at 1600℃ achieved a removal efficiency of over 99.5% for submicron particles in flue gas, with a stable filtration pressure drop of 3.0 kPa.

[0107] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and variations of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A method for preparing mullite fiber porous ceramics, characterized in that, Includes the following steps: The aluminum source compound and silicon micro powder are mixed evenly to obtain a mixed powder; the aluminum source compound is any one of γ-Al2O3 and Al(OH)3 and a mixture of ρ-Al2O3; In ρ-Al2O3, the amount of aluminum accounts for 25% to 75% of the amount of aluminum in the aluminum source compound; Hydroxypropyl methylcellulose aqueous solution, mixed powder and mullite fiber were mixed evenly to obtain a slurry; the slurry was molded using the gel casting method to obtain a sample; The sample was first kept at a first temperature in an air atmosphere to allow the grains to grow, and then the temperature was raised to a second temperature to promote the development of the mullite crystal phase, thus obtaining mullite porous ceramics.

2. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, The amount of aluminum in ρ-Al2O3 accounts for 50% of the amount of aluminum in the aluminum source compound.

3. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, γ-Al2O3 is obtained by calcining Al(OH)3 in an air atmosphere.

4. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, The mass ratio of ρ-Al2O3 to hydroxypropyl methylcellulose is 9~27:0.

2.

5. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, The mass ratio of ρ-Al2O3 to silicon micropowder is 9~27:

14.

6. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, The mass ratio of ρ-Al2O3 to mullite fiber is 9~27:

25.

7. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, The first temperature is 1400℃, and the holding time at the first temperature is 2 hours.

8. The method for preparing a mullite fiber porous ceramic according to claim 1, characterized in that, The second temperature is 1500℃~1600℃, and the holding time at the second temperature is 5h.

9. A mullite fiber porous ceramic prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the mullite fiber porous ceramic of claim 9 as a flue gas filter material in flue gas particulate matter filtration.

Images