Method for preparing ordered structure mullite fiber thermal insulation material by electric field assistance

Abstract

The present application relates to the technical field of fibrous thermal insulation materials, and particularly relates to a method for preparing ordered structure mullite fibrous thermal insulation materials by electric field assistance. The present application comprises the following steps: step 1, slurry preparation, short-cut mullite fibers are dispersed into a mixed solution composed of deionized water and silica sol to form a slurry; step 2, building of a product pool with electric field and application of electric field: step 2-1, determination of electric field parameter, the power voltage ranges from 50 to 90 V, and the electric field intensity ranges from 5000 to 9000 V / m; step 2-2, building of the product pool with electric field; step 2-3, application of electric field, to ensure that all fibers complete rotation in the electric field; step 3, pressing forming, to obtain a wet blank; and step 4, freezing and freeze-drying, to obtain a solid green body. Through the above method, the problem of difficult preparation of ordered structure ceramic fibrous materials is solved, and the present application constructs ordered structure mullite fibrous thermal insulation materials, effectively improving the mechanical properties and thermal insulation performance of the materials.

Description

Technical Field

[0001] This invention relates to the field of fibrous thermal insulation materials, and in particular to a method for preparing ordered mullite fibrous thermal insulation materials with electric field assistance. Background Technology

[0002] To address the brittleness of traditional ceramic aerogels, high-performance ceramic fibrous materials can be constructed using one-dimensional flexible fibers as a matrix. Ceramic fibrous materials are renowned for their low density, low thermal conductivity, and excellent chemical and thermal stability, demonstrating great potential as high-temperature insulation materials. However, assembling one-dimensional fibers on a three-dimensional macroscopic scale without sacrificing their mechanical and thermal properties is crucial for preparing lightweight, high-mechanical-performance, and high-temperature insulation materials. Disordered structures formed by randomly distributed fibers and quasi-ordered structures formed by stacked fiber membranes are currently the two most common structures for fibrous materials. In addition, fibers can also be used to construct highly ordered structures. Ordered ceramic fibrous materials with sufficient mechanical stability, flexibility, and excellent high-temperature resistance are the primary guarantee for effective insulation in extreme environments. However, due to the difficulties in fabrication, there is currently limited research on methods and properties for constructing ordered structures from fibers.

[0003] Previous methods for forming ceramic fibrous materials, including vacuum filtration, sol-gel, cryogenic molding, and spinning, have produced materials with disordered or pseudo-ordered structures. These methods cannot produce materials with highly ordered fiber orientations. Electric field induction can not only obtain highly oriented fibrous materials but also has low requirements on the material itself; many materials have been proven to align in an electric field. Therefore, electric fields are a potentially effective method for preparing ordered fibrous materials. However, for electrically neutral ceramic fibers, very high voltages are often required to rotate the fibers, which increases energy consumption and the risk factor. Summary of the Invention

[0004] To address the difficulty in preparing ordered ceramic fibrous materials, this invention provides a method for preparing ordered mullite fibrous thermal insulation materials using an electric field-assisted process.

[0005] A method for preparing ordered mullite fibrous thermal insulation material with electric field assistance is carried out according to the following steps:

[0006] Step 1: Prepare the slurry:

[0007] Short-cut mullite fibers are dispersed into a mixed solution consisting of deionized water and silica sol, and stirred for a certain period of time to ensure thorough and uniform mixing, thus forming a slurry.

[0008] Step 2: Constructing and applying an electric field to the product cell:

[0009] Step 2-1: Determine the parameters of the applied electric field:

[0010] Determine the power supply voltage and electric field strength for applying the electric field, where the power supply voltage ranges from 50 to 90V and the electric field strength ranges from 5000 to 9000V / m;

[0011] Step 2-2, Construction of the electric field product cell:

[0012] Assemble the product pool using materials. The product pool is a rectangular tank with an open upper surface. Fix two electrode plates to two parallel sides inside the product pool, and then connect wires to the top of the electrode plates. The distance between the two electrode plates is determined based on the power supply voltage and electric field strength.

[0013] Steps 2-3: Apply an electric field:

[0014] Pour the slurry into the product tank and stir for a certain period of time. Connect the two wires to the power source respectively, apply an electric field to the slurry for a certain period of time to ensure that all fibers complete the rotation in the electric field, and then turn off the power.

[0015] Step 3, Pressing and Shaping:

[0016] Place a perforated pressing sheet on top of the product tank, press the pressing sheet down, and then suck out the excess slurry to obtain a wet blank;

[0017] Step 4, Freezing and freeze-drying:

[0018] The product tank is placed in a cold trap to ensure that the slurry is completely frozen, and then the product tank is placed in a freeze dryer for freeze drying to obtain a solid green body.

[0019] Furthermore, in step 1, the mullite fiber has a diameter of 1-6 μm and a length of 100-500 μm; the weight ratio of mullite fiber, silica sol, and deionized water is 0.01-0.02:0.05:1.

[0020] Further, in step 1, the specific preparation method of the silica sol is as follows: First, tetraethyl orthosilicate is poured into a container, anhydrous ethanol is added, then deionized water and a small amount of hydrochloric acid aqueous solution are added to form a mixture. The mixture is placed in a water bath at 50°C and kept warm for 1 hour to obtain silica sol; the concentration of the hydrochloric acid aqueous solution is 0.2 mol / L; the molar ratio of tetraethyl orthosilicate to deionized water is 1:4; the molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:(4~8); the molar ratio of tetraethyl orthosilicate to hydrogen chloride in the hydrochloric acid aqueous solution is 1:(7.5×10⁻⁶). -4 ~15×10 -4 ).

[0021] Furthermore, in step 2-2, the distance between the two electrode plates is 0.95 to 1.05 cm.

[0022] Furthermore, the electric field is applied for a duration of more than 5 minutes in steps 2-3.

[0023] Furthermore, in step 2-2, the length of the product pool is 7.9–8.1 cm, the width is 1.1–1.3 cm, and the height is 7.9–8.1 cm; the length of the electrode sheet is 7.9–8.1 cm, the height is 9.9–10.1 cm, the thickness is 0.9–1.1 mm, and the volume of the product pool is 63–65 cm³. 3 .

[0024] Furthermore, the electrode sheet in step 2-2 is a graphite electrode sheet.

[0025] Furthermore, the power supply in step 2-1 is a DC power supply.

[0026] Furthermore, the pressing sheet in step 3 is an acrylic sheet with holes and a thickness of 0.9 to 1.1 mm.

[0027] Furthermore, the specific process of freezing and freeze-drying in step 4 is as follows: the product pool is placed in a cold trap and frozen at -40°C to -50°C for 6 to 8 hours to ensure that the slurry is completely frozen; then the product pool is placed in a freeze dryer and freeze-dried at -40°C to -50°C and a vacuum of 20Pa to 70Pa for 3 to 5 days to ensure that all ice crystals in the green body sublimate and obtain a solid green body.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] This invention introduces an electric field into a fiber suspension to induce fiber orientation, thereby achieving control over the alignment direction of one-dimensional mullite fibers.

[0030] The product pool designed in this invention does not require a high-voltage power supply. It can obtain a high electric field strength (5000-9000V / m) under low voltage conditions (50-90V), which is energy-saving and safer.

[0031] This invention constructs an ordered structure of mullite fiber thermal insulation material, which effectively improves the mechanical properties of the material.

[0032] The ordered mullite fibrous material prepared by this invention has a low density (0.04–0.08 g / cm³). 3 Low thermal conductivity: 0.032 W / (m·K)~0.037 W / (m·K). Attached Figure Description

[0033] Figure 1 The image shows a SEM image of the mullite fibrous material with a fiber content of 1.12 g prepared in Experiment 1. Figure 1(a) is an article in which no electric field is applied. Figure 1 (b) An article to which an electric field is applied.

[0034] Figure 2 Strength diagrams of mullite fiber materials with different fiber contents prepared for Experiment 1.

[0035] Figure 3 Modulus diagram of mullite fibrous materials with different fiber contents prepared for Experiment 1.

[0036] Figure 4 Thermal conductivity and density diagrams of mullite fibrous materials with different fiber contents prepared for Experiment 1.

[0037] Figure 5 High-temperature thermal conductivity diagram of mullite fiber material with a fiber content of 1.12g prepared for Experiment 1. Detailed Implementation

[0038] Specific Implementation Method 1: This implementation method is a method for preparing ordered mullite fiber thermal insulation material with electric field assistance, specifically carried out according to the following steps:

[0039] Step 1: Prepare the slurry:

[0040] Short-cut mullite fibers are dispersed in a mixed solution consisting of deionized water and silica sol, and stirred with a glass rod for a certain period of time to ensure thorough mixing and form a slurry.

[0041] The mullite fibers have a diameter of 1–6 μm and a length of 100–500 μm. The weight ratio of mullite fibers, silica sol, and deionized water is 0.01–0.02:0.05:1.

[0042] Step 2: Constructing and applying an electric field to the product cell:

[0043] Step 2-1: Determine the parameters of the applied electric field:

[0044] Determine the power supply voltage and electric field strength for applying the electric field; wherein the power supply voltage ranges from 50 to 90V, and the electric field strength ranges from 5000 to 9000V / m.

[0045] For electrically neutral ceramic fibers, according to the theoretical formula of field torque, only by increasing the electric field strength can the ceramic fibers be oriented in the electric field. However, excessively high voltage or excessively high electric field strength will cause the electrode sheet to generate heat, which will have an adverse effect on the slurry. Therefore, the electric field strength should be selected within an appropriate range.

[0046] Step 2-2, Construction of the electric field product cell:

[0047] Assemble the product pool using materials. The product pool is a rectangular tank with an open upper surface. Fix two electrode plates to two parallel sides inside the product pool, and then connect wires to the top of the electrode plates. The distance between the two electrode plates is determined based on the power supply voltage and electric field strength.

[0048] According to the formula E=U / D, where E is the electric field strength, U is the voltage, and D is the perpendicular distance along the direction of the electric field lines, the preferred distance between the electrode plates is 0.95~1.05cm, so that a high electric field strength (5000~9000V / m) can be output under low voltage conditions (50~90V).

[0049] The width of the product pool can be determined based on the distance between the electrode plates and the thickness of the electrode plates; the length and height of the product pool can be determined based on the size of the product. Acrylic sheets or glass can be used as the material for assembling the product pool.

[0050] Steps 2-3: Apply an electric field: Pour the slurry into the product tank and stir for a certain period of time. Connect the two wires to the power source respectively, apply an electric field to the slurry for a certain period of time, and ensure that all fibers complete the rotation in the electric field. Then turn off the power.

[0051] It takes a certain amount of time for the fiber to rotate in the electric field until the fiber axis is parallel to the direction of the electric field. Theoretical calculations show that the theoretical alignment time for a single fiber is 6 to 20 seconds. Considering the interaction between multiple fibers and the effect of the solution on the fibers, the electric field application time in this step should be greater than 5 minutes to ensure that all fibers are aligned with the direction of the electric field without consuming too much energy.

[0052] Preferably, a DC power supply with a voltage of 63–65V is used, at which point the electric field strength is approximately 6350–6450V / m, and the distance between the electrode plates is 0.95–1.05cm. A product tank with a length of 7.9–8.1cm, a width of 1.1–1.3cm, and a height of 7.9–8.1cm is assembled from acrylic sheets. The product tank is a rectangular trough with an open upper surface; the volume of the product tank is 63–65cm³. 3 Two electrode plates, each 7.9–8.1 cm long, 9.9–10.1 cm high, and 0.9–1.1 mm thick, are fixed to the inside of the product tank using double-sided tape. Insulating tape is used to connect the wires to the top of the electrode plates. The slurry is poured into the product tank and stirred for 0.5–1 minute. An electric field is then applied for 9–11 minutes, ensuring that all fibers rotate within the electric field and that the fiber axes are aligned with the direction of the electric field. Afterward, the power is turned off, the connecting wires are disconnected, and the electrode plates remain in the product tank.

[0053] Step 3, Pressing and Shaping:

[0054] A perforated pressing sheet wrapped in gauze is placed on top of the product tank and pressed down to a distance of 1.9–2.1 cm from the bottom of the tank. Excess slurry is then sucked out through a suction tube to obtain a wet preform. The purpose of this step is to maintain fiber alignment. The pressing sheet is a perforated acrylic plate with a thickness of 0.9–1.1 mm.

[0055] Step 4, Freezing and freeze-drying:

[0056] The product tank is placed in a cold trap and frozen at -40°C to -50°C for 6 to 8 hours to ensure complete freezing of the slurry. Subsequently, the product tank is placed in a freeze dryer and freeze-dried at -40°C to -50°C and a vacuum of 20 Pa to 70 Pa for 3 to 5 days to ensure that all ice crystals in the green body sublimate, thus obtaining a solid green body.

[0057] In step 1 of this invention, by changing the content of added fibers, ordered mullite fibrous materials with different fiber contents, i.e. different densities, can be obtained.

[0058] For ease of description, the ordered structure product prepared after applying an electric field is named OR-MF, where OR-MF-z is along the axial direction. The pseudo-ordered structure product without an applied electric field is named QU-MF, where QU-MF-z is along the axial direction and QU-MF-x is along the radial direction.

[0059] The addition of an electric field alters the orientation of the fibers, causing them to align along the direction of the electric field. This improves the overall orderliness of the material, thereby enhancing its mechanical and thermal insulation properties.

[0060] Specific Implementation Method Two: The specific preparation method of the silica sol in step 1 is as follows: First, pour tetraethyl orthosilicate into a container, add anhydrous ethanol, then add deionized water and a small amount of hydrochloric acid aqueous solution to form a mixture. Place the mixture in a 50°C water bath and keep it warm for 1 hour to obtain silica sol; the concentration of the hydrochloric acid aqueous solution is 0.2 mol / L; the molar ratio of tetraethyl orthosilicate to deionized water is 1:4; the molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:(4~8); the molar ratio of tetraethyl orthosilicate to hydrogen chloride in the hydrochloric acid aqueous solution is 1:(7.5×10⁻⁶). -4 ~15×10 -4 Everything else is the same as in Specific Implementation Method 1.

[0061] Specific Implementation Method 3: The electrode sheet mentioned in step 2 is a graphite electrode sheet, and the rest is the same as in Specific Implementation Method 1.

[0062] The invention was verified using the following experiments.

[0063] Experiment 1: This experiment demonstrates a method for preparing ordered mullite fiber thermal insulation materials using an electric field-assisted process. The specific steps are as follows:

[0064] Step 1: Prepare the slurry:

[0065] Short-cut mullite fibers were dispersed in a mixed solution consisting of deionized water and silica sol, and stirred with a glass rod for 1–2 minutes to ensure thorough mixing and form a slurry. The weights of the mullite fibers, silica sol, and deionized water were 0.64–1.28 g, 3.2 g, and 64 g, respectively.

[0066] The specific preparation method of the above-mentioned silica sol is as follows: First, tetraethyl orthosilicate is poured into a beaker, anhydrous ethanol is added, and then deionized water and hydrochloric acid aqueous solution are added to form a mixture. The mixture is placed in a water bath at 50°C and kept warm for 1 hour to obtain silica sol. The concentration of the hydrochloric acid aqueous solution is 0.2 mol / L; the molar ratio of tetraethyl orthosilicate to deionized water is 1:4; the molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:4; and the molar ratio of tetraethyl orthosilicate to hydrogen chloride in the hydrochloric acid aqueous solution is 1:7.5 × 10⁻⁶. -4 ;

[0067] Step 2: Constructing and applying an electric field to the product cell:

[0068] Step 2-1: Determine the parameters of the applied electric field: Use a DC power supply with an output voltage of 64V and an electric field strength of 6400V / m;

[0069] Step 2-2: Construction of the electric field product cell: The distance between the electrode plates is 1cm; assemble a product cell with a length of 8cm, a width of 1.2cm, and a height of 8cm using acrylic plates. The product cell is a rectangular trough with an open upper surface, and its volume is 64cm³. 3 Two electrode plates, each 8cm long, 10cm high, and 1mm thick, are fixed to the inside of the product pool using double-sided tape. Insulating tape is used to connect the wires to the top of the electrode plates.

[0070] Steps 2-3: Apply an electric field: Pour the slurry into the product tank and stir for 1 minute. Connect the two wires to the positive and negative terminals of the power supply respectively. Apply an electric field to the slurry for 10 minutes to ensure that all fibers complete rotation in the electric field. Then turn off the power, pull out the connected wires, and leave the electrode plate in the product tank.

[0071] Step 3, Pressing and Shaping:

[0072] A perforated pressing sheet wrapped in gauze is placed on top of the product pool and pressed down to 2cm from the bottom of the pool. Excess slurry is then sucked out through a suction tube to obtain a wet blank. The pressing sheet is a 1mm thick perforated acrylic sheet.

[0073] Step 4, Freezing and freeze-drying:

[0074] The product tank was placed in a cold trap and frozen at -45°C for 8 hours to ensure the slurry was completely frozen. Subsequently, the product tank was placed in a freeze dryer and freeze-dried at -45°C and a vacuum of 50 Pa for 5 days to ensure that all ice crystals in the green body sublimated, thus obtaining a solid green body.

[0075] Experimental results:

[0076] In step 1 of this experiment, five ordered mullite fiber thermal insulation materials with different densities were obtained by changing the content of mullite fibers to 0.64g, 0.80g, 0.96g, 1.12g, and 1.28g.

[0077] Figure 1 The image shows a SEM image of the mullite fibrous material with a fiber content of 1.12 g prepared in Experiment 1. Figure 1 (a) is an article in which no electric field is applied. Figure 1 (b) The product with an applied electric field. As shown in the figure, in the product without an applied electric field, most of the fibers are randomly distributed, while after an electric field is applied, the fibers are basically arranged neatly along the direction of the electric field. When the fibers are in an electric field, the different electrical properties of the fibers and the solution induce electric dipoles on the fibers. The interaction between these electric dipoles and the electric field induces a field-induced torque on the fibers, causing the fibers to rotate along the direction of the electric field.

[0078] Figure 2 The figure shows the strength of mullite fibrous materials with different fiber contents prepared for Experiment 1. As shown in the figure, the mechanical strength of the products was significantly improved after applying an electric field, and the compressive strength of OR-MF-z products with different fiber contents was higher than that of QU-MF-z products.

[0079] Figure 3 The figure shows the modulus of mullite fibrous materials with different fiber contents prepared for Experiment 1. As shown in the figure, the modulus of the products was significantly improved after applying an electric field, and the modulus of OR-MF-z products with different fiber contents was higher than that of QU-MF-z products.

[0080] Figure 4 The thermal conductivity and density diagrams for the mullite fibrous material prepared for Experiment 1 are shown. As the fiber content increases, the density of the product gradually increases, remaining between 0.04 and 0.08 g / cm³. 3 Within the low-density range, as the fiber content increases, the solid-phase thermal conductivity increases, causing the thermal conductivity of the product to gradually rise, generally remaining between 0.032 and 0.038 W / m. -1 K -1Within the low thermal conductivity range. At the same fiber content, the thermal conductivity of OR-MF-z products is almost similar to that of QU-MF-z products, indicating that the structural rearrangement of fibers does not affect their main heat transfer mode.

[0081] Figure 5 The figure shows the high-temperature thermal conductivity of the mullite fiber material with a fiber content of 1.12g prepared for Experiment 1. As shown in the figure, the fiber orientation has almost no effect on its high-temperature thermal conductivity, and the high-temperature thermal conductivity of the OR-MF-z product remains in a low range, indicating that it has good high-temperature insulation capabilities.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ordered mullite fibrous thermal insulation materials with electric field assistance, characterized in that... Follow these steps: Step 1: Prepare the slurry: Short-cut mullite fibers are dispersed into a mixed solution consisting of deionized water and silica sol, and stirred for a certain period of time to ensure thorough mixing and form a slurry. Step 2: Constructing and applying an electric field to the product cell: Step 2-1: Determine the parameters of the applied electric field: Determine the power supply voltage and electric field strength for applying the electric field, where the power supply voltage ranges from 50 to 90V and the electric field strength ranges from 5000 to 9000V / m; Step 2-2, Construction of the electric field product cell: Assemble the product pool using materials. The product pool is a rectangular tank with an open upper surface. Fix two electrode plates to two parallel sides inside the product pool, and then connect wires to the top of the electrode plates. The distance between the two electrode plates is determined based on the power supply voltage and electric field strength. The distance between the two electrode plates is 0.95–1.05 cm; Steps 2-3: Apply an electric field: Pour the slurry into the product tank and stir for a certain period of time. Connect the two wires to the power source respectively, apply an electric field to the slurry for a certain period of time to ensure that all fibers complete the rotation in the electric field, and then turn off the power. Step 3, Pressing and Shaping: Place a perforated pressing sheet on top of the product tank, press the pressing sheet down, and then suck out the excess slurry to obtain a wet blank; Step 4, Freezing and freeze-drying: The product tank is placed in a cold trap to ensure that the slurry is completely frozen. Then, the product tank is placed in a freeze dryer for freeze drying to obtain a solid green body.

2. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, In step 1, the mullite fiber has a diameter of 1-6 μm and a length of 100-500 μm; the weight ratio of mullite fiber, silica sol and deionized water is 0.01-0.02:0.05:

1.

3. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, In step 1, the specific preparation method of silica sol is as follows: First, tetraethyl orthosilicate is poured into a container, anhydrous ethanol is added, then deionized water and a small amount of hydrochloric acid aqueous solution are added to form a mixture. The mixture is placed in a water bath at 50°C and kept warm for 1 hour to obtain silica sol. The concentration of the hydrochloric acid aqueous solution is 0.2 mol / L; the molar ratio of tetraethyl orthosilicate to deionized water is 1:4; the molar ratio of tetraethyl orthosilicate to anhydrous ethanol is 1:(4~8); the molar ratio of tetraethyl orthosilicate to hydrogen chloride in the hydrochloric acid aqueous solution is 1:(7.5×10⁻⁶). -4 ~15×10 -4 ).

4. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, The electric field is applied for a duration of more than 5 minutes in steps 2-3.

5. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, In step 2-2, the product pool has a length of 7.9–8.1 cm, a width of 1.1–1.3 cm, and a height of 7.9–8.1 cm; the electrode sheet has a length of 7.9–8.1 cm, a height of 9.9–10.1 cm, and a thickness of 0.9–1.1 mm; the volume of the product pool is 63–65 cm³. 3 .

6. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, The electrode sheet in step 2-2 is a graphite electrode sheet.

7. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, The power source in step 2-1 is a DC power source.

8. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, The pressing sheet in step 3 is an acrylic sheet with holes and a thickness of 0.9 to 1.1 mm.

9. The method for preparing ordered mullite fibrous thermal insulation material with electric field assistance according to claim 1, characterized in that, The specific process of freezing and freeze-drying in step 4 is as follows: the product pool is placed in a cold trap and frozen at -40°C to -50°C for 6 to 8 hours to ensure that the slurry is completely frozen; then the product pool is placed in a freeze dryer and freeze-dried at -40°C to -50°C and a vacuum of 20Pa to 70Pa for 3 to 5 days to ensure that all the ice crystals in the green body sublimate and obtain a solid green body.

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